text: /* SPDX-License-Identifier: GPL-2.0-or-later */
  /*
   *	Definitions for the 'struct sk_buff' memory handlers.
   *
   *	Authors:
   *		Alan Cox, <gw4pts@gw4pts.ampr.org>
   *		Florian La Roche, <rzsfl@rz.uni-sb.de>
   */
  
  #ifndef _LINUX_SKBUFF_H
  #define _LINUX_SKBUFF_H
  
  #include <linux/kernel.h>
  #include <linux/compiler.h>
  #include <linux/time.h>
  #include <linux/bug.h>
  #include <linux/bvec.h>
  #include <linux/cache.h>
  #include <linux/rbtree.h>
  #include <linux/socket.h>
  #include <linux/refcount.h>
  
  #include <linux/atomic.h>
  #include <asm/types.h>
  #include <linux/spinlock.h>
  #include <linux/net.h>
  #include <linux/textsearch.h>
  #include <net/checksum.h>
  #include <linux/rcupdate.h>
  #include <linux/hrtimer.h>
  #include <linux/dma-mapping.h>
  #include <linux/netdev_features.h>
  #include <linux/sched.h>
  #include <linux/sched/clock.h>
  #include <net/flow_dissector.h>
  #include <linux/splice.h>
  #include <linux/in6.h>
  #include <linux/if_packet.h>
  #include <net/flow.h>
  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  #include <linux/netfilter/nf_conntrack_common.h>
  #endif
  
  /* The interface for checksum offload between the stack and networking drivers
   * is as follows...
   *
   * A. IP checksum related features
   *
   * Drivers advertise checksum offload capabilities in the features of a device.
   * From the stack's point of view these are capabilities offered by the driver.
   * A driver typically only advertises features that it is capable of offloading
   * to its device.
   *
   * The checksum related features are:
   *
   *	NETIF_F_HW_CSUM	- The driver (or its device) is able to compute one
   *			  IP (one's complement) checksum for any combination
   *			  of protocols or protocol layering. The checksum is
   *			  computed and set in a packet per the CHECKSUM_PARTIAL
   *			  interface (see below).
   *
   *	NETIF_F_IP_CSUM - Driver (device) is only able to checksum plain
   *			  TCP or UDP packets over IPv4. These are specifically
   *			  unencapsulated packets of the form IPv4|TCP or
   *			  IPv4|UDP where the Protocol field in the IPv4 header
   *			  is TCP or UDP. The IPv4 header may contain IP options.
   *			  This feature cannot be set in features for a device
   *			  with NETIF_F_HW_CSUM also set. This feature is being
   *			  DEPRECATED (see below).
   *
   *	NETIF_F_IPV6_CSUM - Driver (device) is only able to checksum plain
   *			  TCP or UDP packets over IPv6. These are specifically
   *			  unencapsulated packets of the form IPv6|TCP or
   *			  IPv6|UDP where the Next Header field in the IPv6
   *			  header is either TCP or UDP. IPv6 extension headers
   *			  are not supported with this feature. This feature
   *			  cannot be set in features for a device with
   *			  NETIF_F_HW_CSUM also set. This feature is being
   *			  DEPRECATED (see below).
   *
   *	NETIF_F_RXCSUM - Driver (device) performs receive checksum offload.
   *			 This flag is only used to disable the RX checksum
   *			 feature for a device. The stack will accept receive
   *			 checksum indication in packets received on a device
   *			 regardless of whether NETIF_F_RXCSUM is set.
   *
   * B. Checksumming of received packets by device. Indication of checksum
   *    verification is set in skb->ip_summed. Possible values are:
   *
   * CHECKSUM_NONE:
   *
   *   Device did not checksum this packet e.g. due to lack of capabilities.
   *   The packet contains full (though not verified) checksum in packet but
   *   not in skb->csum. Thus, skb->csum is undefined in this case.
   *
   * CHECKSUM_UNNECESSARY:
   *
   *   The hardware you're dealing with doesn't calculate the full checksum
   *   (as in CHECKSUM_COMPLETE), but it does parse headers and verify checksums
   *   for specific protocols. For such packets it will set CHECKSUM_UNNECESSARY
   *   if their checksums are okay. skb->csum is still undefined in this case
   *   though. A driver or device must never modify the checksum field in the
   *   packet even if checksum is verified.
   *
   *   CHECKSUM_UNNECESSARY is applicable to following protocols:
   *     TCP: IPv6 and IPv4.
   *     UDP: IPv4 and IPv6. A device may apply CHECKSUM_UNNECESSARY to a
   *       zero UDP checksum for either IPv4 or IPv6, the networking stack
   *       may perform further validation in this case.
   *     GRE: only if the checksum is present in the header.
   *     SCTP: indicates the CRC in SCTP header has been validated.
   *     FCOE: indicates the CRC in FC frame has been validated.
   *
   *   skb->csum_level indicates the number of consecutive checksums found in
   *   the packet minus one that have been verified as CHECKSUM_UNNECESSARY.
   *   For instance if a device receives an IPv6->UDP->GRE->IPv4->TCP packet
   *   and a device is able to verify the checksums for UDP (possibly zero),
   *   GRE (checksum flag is set) and TCP, skb->csum_level would be set to
   *   two. If the device were only able to verify the UDP checksum and not
   *   GRE, either because it doesn't support GRE checksum or because GRE
   *   checksum is bad, skb->csum_level would be set to zero (TCP checksum is
   *   not considered in this case).
   *
   * CHECKSUM_COMPLETE:
   *
   *   This is the most generic way. The device supplied checksum of the _whole_
   *   packet as seen by netif_rx() and fills in skb->csum. This means the
   *   hardware doesn't need to parse L3/L4 headers to implement this.
   *
   *   Notes:
   *   - Even if device supports only some protocols, but is able to produce
   *     skb->csum, it MUST use CHECKSUM_COMPLETE, not CHECKSUM_UNNECESSARY.
   *   - CHECKSUM_COMPLETE is not applicable to SCTP and FCoE protocols.
   *
   * CHECKSUM_PARTIAL:
   *
   *   A checksum is set up to be offloaded to a device as described in the
   *   output description for CHECKSUM_PARTIAL. This may occur on a packet
   *   received directly from another Linux OS, e.g., a virtualized Linux kernel
   *   on the same host, or it may be set in the input path in GRO or remote
   *   checksum offload. For the purposes of checksum verification, the checksum
   *   referred to by skb->csum_start + skb->csum_offset and any preceding
   *   checksums in the packet are considered verified. Any checksums in the
   *   packet that are after the checksum being offloaded are not considered to
   *   be verified.
   *
   * C. Checksumming on transmit for non-GSO. The stack requests checksum offload
   *    in the skb->ip_summed for a packet. Values are:
   *
   * CHECKSUM_PARTIAL:
   *
   *   The driver is required to checksum the packet as seen by hard_start_xmit()
   *   from skb->csum_start up to the end, and to record/write the checksum at
   *   offset skb->csum_start + skb->csum_offset. A driver may verify that the
   *   csum_start and csum_offset values are valid values given the length and
   *   offset of the packet, but it should not attempt to validate that the
   *   checksum refers to a legitimate transport layer checksum -- it is the
   *   purview of the stack to validate that csum_start and csum_offset are set
   *   correctly.
   *
   *   When the stack requests checksum offload for a packet, the driver MUST
   *   ensure that the checksum is set correctly. A driver can either offload the
   *   checksum calculation to the device, or call skb_checksum_help (in the case
   *   that the device does not support offload for a particular checksum).
   *
   *   NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM are being deprecated in favor of
   *   NETIF_F_HW_CSUM. New devices should use NETIF_F_HW_CSUM to indicate
   *   checksum offload capability.
   *   skb_csum_hwoffload_help() can be called to resolve CHECKSUM_PARTIAL based
   *   on network device checksumming capabilities: if a packet does not match
   *   them, skb_checksum_help or skb_crc32c_help (depending on the value of
   *   csum_not_inet, see item D.) is called to resolve the checksum.
   *
   * CHECKSUM_NONE:
   *
   *   The skb was already checksummed by the protocol, or a checksum is not
   *   required.
   *
   * CHECKSUM_UNNECESSARY:
   *
   *   This has the same meaning as CHECKSUM_NONE for checksum offload on
   *   output.
   *
   * CHECKSUM_COMPLETE:
   *   Not used in checksum output. If a driver observes a packet with this value
   *   set in skbuff, it should treat the packet as if CHECKSUM_NONE were set.
   *
   * D. Non-IP checksum (CRC) offloads
   *
   *   NETIF_F_SCTP_CRC - This feature indicates that a device is capable of
   *     offloading the SCTP CRC in a packet. To perform this offload the stack
   *     will set csum_start and csum_offset accordingly, set ip_summed to
   *     CHECKSUM_PARTIAL and set csum_not_inet to 1, to provide an indication in
   *     the skbuff that the CHECKSUM_PARTIAL refers to CRC32c.
   *     A driver that supports both IP checksum offload and SCTP CRC32c offload
   *     must verify which offload is configured for a packet by testing the
   *     value of skb->csum_not_inet; skb_crc32c_csum_help is provided to resolve
   *     CHECKSUM_PARTIAL on skbs where csum_not_inet is set to 1.
   *
   *   NETIF_F_FCOE_CRC - This feature indicates that a device is capable of
   *     offloading the FCOE CRC in a packet. To perform this offload the stack
   *     will set ip_summed to CHECKSUM_PARTIAL and set csum_start and csum_offset
   *     accordingly. Note that there is no indication in the skbuff that the
   *     CHECKSUM_PARTIAL refers to an FCOE checksum, so a driver that supports
   *     both IP checksum offload and FCOE CRC offload must verify which offload
   *     is configured for a packet, presumably by inspecting packet headers.
   *
   * E. Checksumming on output with GSO.
   *
   * In the case of a GSO packet (skb_is_gso(skb) is true), checksum offload
   * is implied by the SKB_GSO_* flags in gso_type. Most obviously, if the
   * gso_type is SKB_GSO_TCPV4 or SKB_GSO_TCPV6, TCP checksum offload as
   * part of the GSO operation is implied. If a checksum is being offloaded
   * with GSO then ip_summed is CHECKSUM_PARTIAL, and both csum_start and
   * csum_offset are set to refer to the outermost checksum being offloaded
   * (two offloaded checksums are possible with UDP encapsulation).
   */
  
  /* Don't change this without changing skb_csum_unnecessary! */
  #define CHECKSUM_NONE		0
  #define CHECKSUM_UNNECESSARY	1
  #define CHECKSUM_COMPLETE	2
  #define CHECKSUM_PARTIAL	3
  
  /* Maximum value in skb->csum_level */
  #define SKB_MAX_CSUM_LEVEL	3
  
  #define SKB_DATA_ALIGN(X)	ALIGN(X, SMP_CACHE_BYTES)
  #define SKB_WITH_OVERHEAD(X)	\
  	((X) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
  #define SKB_MAX_ORDER(X, ORDER) \
  	SKB_WITH_OVERHEAD((PAGE_SIZE << (ORDER)) - (X))
  #define SKB_MAX_HEAD(X)		(SKB_MAX_ORDER((X), 0))
  #define SKB_MAX_ALLOC		(SKB_MAX_ORDER(0, 2))
  
  /* return minimum truesize of one skb containing X bytes of data */
  #define SKB_TRUESIZE(X) ((X) +						\
  			 SKB_DATA_ALIGN(sizeof(struct sk_buff)) +	\
  			 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
  
  struct ahash_request;
  struct net_device;
  struct scatterlist;
  struct pipe_inode_info;
  struct iov_iter;
  struct napi_struct;
  struct bpf_prog;
  union bpf_attr;
  struct skb_ext;
  
  #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
  struct nf_bridge_info {
  	enum {
  		BRNF_PROTO_UNCHANGED,
  		BRNF_PROTO_8021Q,
  		BRNF_PROTO_PPPOE
  	} orig_proto:8;
  	u8			pkt_otherhost:1;
  	u8			in_prerouting:1;
  	u8			bridged_dnat:1;
  	__u16			frag_max_size;
  	struct net_device	*physindev;
  
  	/* always valid & non-NULL from FORWARD on, for physdev match */
  	struct net_device	*physoutdev;
  	union {
  		/* prerouting: detect dnat in orig/reply direction */
  		__be32          ipv4_daddr;
  		struct in6_addr ipv6_daddr;
  
  		/* after prerouting + nat detected: store original source
  		 * mac since neigh resolution overwrites it, only used while
  		 * skb is out in neigh layer.
  		 */
  		char neigh_header[8];
  	};
  };
  #endif
  
  #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
  /* Chain in tc_skb_ext will be used to share the tc chain with
   * ovs recirc_id. It will be set to the current chain by tc
   * and read by ovs to recirc_id.
   */
  struct tc_skb_ext {
  	__u32 chain;
  	__u16 mru;
  };
  #endif
  
  struct sk_buff_head {
  	/* These two members must be first. */
  	struct sk_buff	*next;
  	struct sk_buff	*prev;
  
  	__u32		qlen;
  	spinlock_t	lock;
  };
  
  struct sk_buff;
  
  /* To allow 64K frame to be packed as single skb without frag_list we
   * require 64K/PAGE_SIZE pages plus 1 additional page to allow for
   * buffers which do not start on a page boundary.
   *
   * Since GRO uses frags we allocate at least 16 regardless of page
   * size.
   */
  #if (65536/PAGE_SIZE + 1) < 16
  #define MAX_SKB_FRAGS 16UL
  #else
  #define MAX_SKB_FRAGS (65536/PAGE_SIZE + 1)
  #endif
  extern int sysctl_max_skb_frags;
  
  /* Set skb_shinfo(skb)->gso_size to this in case you want skb_segment to
   * segment using its current segmentation instead.
   */
  #define GSO_BY_FRAGS	0xFFFF
  
  typedef struct bio_vec skb_frag_t;
  
  /**
   * skb_frag_size() - Returns the size of a skb fragment
   * @frag: skb fragment
   */
  static inline unsigned int skb_frag_size(const skb_frag_t *frag)
  {
  	return frag->bv_len;
  }
  
  /**
   * skb_frag_size_set() - Sets the size of a skb fragment
   * @frag: skb fragment
   * @size: size of fragment
   */
  static inline void skb_frag_size_set(skb_frag_t *frag, unsigned int size)
  {
  	frag->bv_len = size;
  }
  
  /**
   * skb_frag_size_add() - Increments the size of a skb fragment by @delta
   * @frag: skb fragment
   * @delta: value to add
   */
  static inline void skb_frag_size_add(skb_frag_t *frag, int delta)
  {
  	frag->bv_len += delta;
  }
  
  /**
   * skb_frag_size_sub() - Decrements the size of a skb fragment by @delta
   * @frag: skb fragment
   * @delta: value to subtract
   */
  static inline void skb_frag_size_sub(skb_frag_t *frag, int delta)
  {
  	frag->bv_len -= delta;
  }
  
  /**
   * skb_frag_must_loop - Test if %p is a high memory page
   * @p: fragment's page
   */
  static inline bool skb_frag_must_loop(struct page *p)
  {
  #if defined(CONFIG_HIGHMEM)
  	if (PageHighMem(p))
  		return true;
  #endif
  	return false;
  }
  
  /**
   *	skb_frag_foreach_page - loop over pages in a fragment
   *
   *	@f:		skb frag to operate on
   *	@f_off:		offset from start of f->bv_page
   *	@f_len:		length from f_off to loop over
   *	@p:		(temp var) current page
   *	@p_off:		(temp var) offset from start of current page,
   *	                           non-zero only on first page.
   *	@p_len:		(temp var) length in current page,
   *				   < PAGE_SIZE only on first and last page.
   *	@copied:	(temp var) length so far, excluding current p_len.
   *
   *	A fragment can hold a compound page, in which case per-page
   *	operations, notably kmap_atomic, must be called for each
   *	regular page.
   */
  #define skb_frag_foreach_page(f, f_off, f_len, p, p_off, p_len, copied)	\
  	for (p = skb_frag_page(f) + ((f_off) >> PAGE_SHIFT),		\
  	     p_off = (f_off) & (PAGE_SIZE - 1),				\
  	     p_len = skb_frag_must_loop(p) ?				\
  	     min_t(u32, f_len, PAGE_SIZE - p_off) : f_len,		\
  	     copied = 0;						\
  	     copied < f_len;						\
  	     copied += p_len, p++, p_off = 0,				\
  	     p_len = min_t(u32, f_len - copied, PAGE_SIZE))		\
  
  #define HAVE_HW_TIME_STAMP
  
  /**
   * struct skb_shared_hwtstamps - hardware time stamps
   * @hwtstamp:	hardware time stamp transformed into duration
   *		since arbitrary point in time
   *
   * Software time stamps generated by ktime_get_real() are stored in
   * skb->tstamp.
   *
   * hwtstamps can only be compared against other hwtstamps from
   * the same device.
   *
   * This structure is attached to packets as part of the
   * &skb_shared_info. Use skb_hwtstamps() to get a pointer.
   */
  struct skb_shared_hwtstamps {
  	ktime_t	hwtstamp;
  };
  
  /* Definitions for tx_flags in struct skb_shared_info */
  enum {
  	/* generate hardware time stamp */
  	SKBTX_HW_TSTAMP = 1 << 0,
  
  	/* generate software time stamp when queueing packet to NIC */
  	SKBTX_SW_TSTAMP = 1 << 1,
  
  	/* device driver is going to provide hardware time stamp */
  	SKBTX_IN_PROGRESS = 1 << 2,
  
  	/* device driver supports TX zero-copy buffers */
  	SKBTX_DEV_ZEROCOPY = 1 << 3,
  
  	/* generate wifi status information (where possible) */
  	SKBTX_WIFI_STATUS = 1 << 4,
  
  	/* This indicates at least one fragment might be overwritten
  	 * (as in vmsplice(), sendfile() ...)
  	 * If we need to compute a TX checksum, we'll need to copy
  	 * all frags to avoid possible bad checksum
  	 */
  	SKBTX_SHARED_FRAG = 1 << 5,
  
  	/* generate software time stamp when entering packet scheduling */
  	SKBTX_SCHED_TSTAMP = 1 << 6,
  };
  
  #define SKBTX_ZEROCOPY_FRAG	(SKBTX_DEV_ZEROCOPY | SKBTX_SHARED_FRAG)
  #define SKBTX_ANY_SW_TSTAMP	(SKBTX_SW_TSTAMP    | \
  				 SKBTX_SCHED_TSTAMP)
  #define SKBTX_ANY_TSTAMP	(SKBTX_HW_TSTAMP | SKBTX_ANY_SW_TSTAMP)
  
  /*
   * The callback notifies userspace to release buffers when skb DMA is done in
   * lower device, the skb last reference should be 0 when calling this.
   * The zerocopy_success argument is true if zero copy transmit occurred,
   * false on data copy or out of memory error caused by data copy attempt.
   * The ctx field is used to track device context.
   * The desc field is used to track userspace buffer index.
   */
  struct ubuf_info {
  	void (*callback)(struct ubuf_info *, bool zerocopy_success);
  	union {
  		struct {
  			unsigned long desc;
  			void *ctx;
  		};
  		struct {
  			u32 id;
  			u16 len;
  			u16 zerocopy:1;
  			u32 bytelen;
  		};
  	};
  	refcount_t refcnt;
  
  	struct mmpin {
  		struct user_struct *user;
  		unsigned int num_pg;
  	} mmp;
  };
  
  #define skb_uarg(SKB)	((struct ubuf_info *)(skb_shinfo(SKB)->destructor_arg))
  
  int mm_account_pinned_pages(struct mmpin *mmp, size_t size);
  void mm_unaccount_pinned_pages(struct mmpin *mmp);
  
  struct ubuf_info *sock_zerocopy_alloc(struct sock *sk, size_t size);
  struct ubuf_info *sock_zerocopy_realloc(struct sock *sk, size_t size,
  					struct ubuf_info *uarg);
  
  static inline void sock_zerocopy_get(struct ubuf_info *uarg)
  {
  	refcount_inc(&uarg->refcnt);
  }
  
  void sock_zerocopy_put(struct ubuf_info *uarg);
  void sock_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref);
  
  void sock_zerocopy_callback(struct ubuf_info *uarg, bool success);
  
  int skb_zerocopy_iter_dgram(struct sk_buff *skb, struct msghdr *msg, int len);
  int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
  			     struct msghdr *msg, int len,
  			     struct ubuf_info *uarg);
  
  /* This data is invariant across clones and lives at
   * the end of the header data, ie. at skb->end.
   */
  struct skb_shared_info {
  	__u8		__unused;
  	__u8		meta_len;
  	__u8		nr_frags;
  	__u8		tx_flags;
  	unsigned short	gso_size;
  	/* Warning: this field is not always filled in (UFO)! */
  	unsigned short	gso_segs;
  	struct sk_buff	*frag_list;
  	struct skb_shared_hwtstamps hwtstamps;
  	unsigned int	gso_type;
  	u32		tskey;
  
  	/*
  	 * Warning : all fields before dataref are cleared in __alloc_skb()
  	 */
  	atomic_t	dataref;
  
  	/* Intermediate layers must ensure that destructor_arg
  	 * remains valid until skb destructor */
  	void *		destructor_arg;
  
  	/* must be last field, see pskb_expand_head() */
  	skb_frag_t	frags[MAX_SKB_FRAGS];
  };
  
  /* We divide dataref into two halves.  The higher 16 bits hold references
   * to the payload part of skb->data.  The lower 16 bits hold references to
   * the entire skb->data.  A clone of a headerless skb holds the length of
   * the header in skb->hdr_len.
   *
   * All users must obey the rule that the skb->data reference count must be
   * greater than or equal to the payload reference count.
   *
   * Holding a reference to the payload part means that the user does not
   * care about modifications to the header part of skb->data.
   */
  #define SKB_DATAREF_SHIFT 16
  #define SKB_DATAREF_MASK ((1 << SKB_DATAREF_SHIFT) - 1)
  
  
  enum {
  	SKB_FCLONE_UNAVAILABLE,	/* skb has no fclone (from head_cache) */
  	SKB_FCLONE_ORIG,	/* orig skb (from fclone_cache) */
  	SKB_FCLONE_CLONE,	/* companion fclone skb (from fclone_cache) */
  };
  
  enum {
  	SKB_GSO_TCPV4 = 1 << 0,
  
  	/* This indicates the skb is from an untrusted source. */
  	SKB_GSO_DODGY = 1 << 1,
  
  	/* This indicates the tcp segment has CWR set. */
  	SKB_GSO_TCP_ECN = 1 << 2,
  
  	SKB_GSO_TCP_FIXEDID = 1 << 3,
  
  	SKB_GSO_TCPV6 = 1 << 4,
  
  	SKB_GSO_FCOE = 1 << 5,
  
  	SKB_GSO_GRE = 1 << 6,
  
  	SKB_GSO_GRE_CSUM = 1 << 7,
  
  	SKB_GSO_IPXIP4 = 1 << 8,
  
  	SKB_GSO_IPXIP6 = 1 << 9,
  
  	SKB_GSO_UDP_TUNNEL = 1 << 10,
  
  	SKB_GSO_UDP_TUNNEL_CSUM = 1 << 11,
  
  	SKB_GSO_PARTIAL = 1 << 12,
  
  	SKB_GSO_TUNNEL_REMCSUM = 1 << 13,
  
  	SKB_GSO_SCTP = 1 << 14,
  
  	SKB_GSO_ESP = 1 << 15,
  
  	SKB_GSO_UDP = 1 << 16,
  
  	SKB_GSO_UDP_L4 = 1 << 17,
  
  	SKB_GSO_FRAGLIST = 1 << 18,
  };
  
  #if BITS_PER_LONG > 32
  #define NET_SKBUFF_DATA_USES_OFFSET 1
  #endif
  
  #ifdef NET_SKBUFF_DATA_USES_OFFSET
  typedef unsigned int sk_buff_data_t;
  #else
  typedef unsigned char *sk_buff_data_t;
  #endif
  
  /**
   *	struct sk_buff - socket buffer
   *	@next: Next buffer in list
   *	@prev: Previous buffer in list
   *	@tstamp: Time we arrived/left
   *	@skb_mstamp_ns: (aka @tstamp) earliest departure time; start point
   *		for retransmit timer
   *	@rbnode: RB tree node, alternative to next/prev for netem/tcp
   *	@list: queue head
   *	@sk: Socket we are owned by
   *	@ip_defrag_offset: (aka @sk) alternate use of @sk, used in
   *		fragmentation management
   *	@dev: Device we arrived on/are leaving by
   *	@dev_scratch: (aka @dev) alternate use of @dev when @dev would be %NULL
   *	@cb: Control buffer. Free for use by every layer. Put private vars here
   *	@_skb_refdst: destination entry (with norefcount bit)
   *	@sp: the security path, used for xfrm
   *	@len: Length of actual data
   *	@data_len: Data length
   *	@mac_len: Length of link layer header
   *	@hdr_len: writable header length of cloned skb
   *	@csum: Checksum (must include start/offset pair)
   *	@csum_start: Offset from skb->head where checksumming should start
   *	@csum_offset: Offset from csum_start where checksum should be stored
   *	@priority: Packet queueing priority
   *	@ignore_df: allow local fragmentation
   *	@cloned: Head may be cloned (check refcnt to be sure)
   *	@ip_summed: Driver fed us an IP checksum
   *	@nohdr: Payload reference only, must not modify header
   *	@pkt_type: Packet class
   *	@fclone: skbuff clone status
   *	@ipvs_property: skbuff is owned by ipvs
   *	@inner_protocol_type: whether the inner protocol is
   *		ENCAP_TYPE_ETHER or ENCAP_TYPE_IPPROTO
   *	@remcsum_offload: remote checksum offload is enabled
   *	@offload_fwd_mark: Packet was L2-forwarded in hardware
   *	@offload_l3_fwd_mark: Packet was L3-forwarded in hardware
   *	@tc_skip_classify: do not classify packet. set by IFB device
   *	@tc_at_ingress: used within tc_classify to distinguish in/egress
   *	@redirected: packet was redirected by packet classifier
   *	@from_ingress: packet was redirected from the ingress path
   *	@peeked: this packet has been seen already, so stats have been
   *		done for it, don't do them again
   *	@nf_trace: netfilter packet trace flag
   *	@protocol: Packet protocol from driver
   *	@destructor: Destruct function
   *	@tcp_tsorted_anchor: list structure for TCP (tp->tsorted_sent_queue)
   *	@_nfct: Associated connection, if any (with nfctinfo bits)
   *	@nf_bridge: Saved data about a bridged frame - see br_netfilter.c
   *	@skb_iif: ifindex of device we arrived on
   *	@tc_index: Traffic control index
   *	@hash: the packet hash
   *	@queue_mapping: Queue mapping for multiqueue devices
   *	@head_frag: skb was allocated from page fragments,
   *		not allocated by kmalloc() or vmalloc().
   *	@pfmemalloc: skbuff was allocated from PFMEMALLOC reserves
   *	@active_extensions: active extensions (skb_ext_id types)
   *	@ndisc_nodetype: router type (from link layer)
   *	@ooo_okay: allow the mapping of a socket to a queue to be changed
   *	@l4_hash: indicate hash is a canonical 4-tuple hash over transport
   *		ports.
   *	@sw_hash: indicates hash was computed in software stack
   *	@wifi_acked_valid: wifi_acked was set
   *	@wifi_acked: whether frame was acked on wifi or not
   *	@no_fcs:  Request NIC to treat last 4 bytes as Ethernet FCS
   *	@encapsulation: indicates the inner headers in the skbuff are valid
   *	@encap_hdr_csum: software checksum is needed
   *	@csum_valid: checksum is already valid
   *	@csum_not_inet: use CRC32c to resolve CHECKSUM_PARTIAL
   *	@csum_complete_sw: checksum was completed by software
   *	@csum_level: indicates the number of consecutive checksums found in
   *		the packet minus one that have been verified as
   *		CHECKSUM_UNNECESSARY (max 3)
   *	@dst_pending_confirm: need to confirm neighbour
   *	@decrypted: Decrypted SKB
   *	@napi_id: id of the NAPI struct this skb came from
   *	@sender_cpu: (aka @napi_id) source CPU in XPS
   *	@secmark: security marking
   *	@mark: Generic packet mark
   *	@reserved_tailroom: (aka @mark) number of bytes of free space available
   *		at the tail of an sk_buff
   *	@vlan_present: VLAN tag is present
   *	@vlan_proto: vlan encapsulation protocol
   *	@vlan_tci: vlan tag control information
   *	@inner_protocol: Protocol (encapsulation)
   *	@inner_ipproto: (aka @inner_protocol) stores ipproto when
   *		skb->inner_protocol_type == ENCAP_TYPE_IPPROTO;
   *	@inner_transport_header: Inner transport layer header (encapsulation)
   *	@inner_network_header: Network layer header (encapsulation)
   *	@inner_mac_header: Link layer header (encapsulation)
   *	@transport_header: Transport layer header
   *	@network_header: Network layer header
   *	@mac_header: Link layer header
   *	@tail: Tail pointer
   *	@end: End pointer
   *	@head: Head of buffer
   *	@data: Data head pointer
   *	@truesize: Buffer size
   *	@users: User count - see {datagram,tcp}.c
   *	@extensions: allocated extensions, valid if active_extensions is nonzero
   */
  
  struct sk_buff {
  	union {
  		struct {
  			/* These two members must be first. */
  			struct sk_buff		*next;
  			struct sk_buff		*prev;
  
  			union {
  				struct net_device	*dev;
  				/* Some protocols might use this space to store information,
  				 * while device pointer would be NULL.
  				 * UDP receive path is one user.
  				 */
  				unsigned long		dev_scratch;
  			};
  		};
  		struct rb_node		rbnode; /* used in netem, ip4 defrag, and tcp stack */
  		struct list_head	list;
  	};
  
  	union {
  		struct sock		*sk;
  		int			ip_defrag_offset;
  	};
  
  	union {
  		ktime_t		tstamp;
  		u64		skb_mstamp_ns; /* earliest departure time */
  	};
  	/*
  	 * This is the control buffer. It is free to use for every
  	 * layer. Please put your private variables there. If you
  	 * want to keep them across layers you have to do a skb_clone()
  	 * first. This is owned by whoever has the skb queued ATM.
  	 */
  	char			cb[48] __aligned(8);
  
  	union {
  		struct {
  			unsigned long	_skb_refdst;
  			void		(*destructor)(struct sk_buff *skb);
  		};
  		struct list_head	tcp_tsorted_anchor;
  	};
  
  #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
  	unsigned long		 _nfct;
  #endif
  	unsigned int		len,
  				data_len;
  	__u16			mac_len,
  				hdr_len;
  
  	/* Following fields are _not_ copied in __copy_skb_header()
  	 * Note that queue_mapping is here mostly to fill a hole.
  	 */
  	__u16			queue_mapping;
  
  /* if you move cloned around you also must adapt those constants */
  #ifdef __BIG_ENDIAN_BITFIELD
  #define CLONED_MASK	(1 << 7)
  #else
  #define CLONED_MASK	1
  #endif
  #define CLONED_OFFSET()		offsetof(struct sk_buff, __cloned_offset)
  
  	/* private: */
  	__u8			__cloned_offset[0];
  	/* public: */
  	__u8			cloned:1,
  				nohdr:1,
  				fclone:2,
  				peeked:1,
  				head_frag:1,
  				pfmemalloc:1;
  #ifdef CONFIG_SKB_EXTENSIONS
  	__u8			active_extensions;
  #endif
  	/* fields enclosed in headers_start/headers_end are copied
  	 * using a single memcpy() in __copy_skb_header()
  	 */
  	/* private: */
  	__u32			headers_start[0];
  	/* public: */
  
  /* if you move pkt_type around you also must adapt those constants */
  #ifdef __BIG_ENDIAN_BITFIELD
  #define PKT_TYPE_MAX	(7 << 5)
  #else
  #define PKT_TYPE_MAX	7
  #endif
  #define PKT_TYPE_OFFSET()	offsetof(struct sk_buff, __pkt_type_offset)
  
  	/* private: */
  	__u8			__pkt_type_offset[0];
  	/* public: */
  	__u8			pkt_type:3;
  	__u8			ignore_df:1;
  	__u8			nf_trace:1;
  	__u8			ip_summed:2;
  	__u8			ooo_okay:1;
  
  	__u8			l4_hash:1;
  	__u8			sw_hash:1;
  	__u8			wifi_acked_valid:1;
  	__u8			wifi_acked:1;
  	__u8			no_fcs:1;
  	/* Indicates the inner headers are valid in the skbuff. */
  	__u8			encapsulation:1;
  	__u8			encap_hdr_csum:1;
  	__u8			csum_valid:1;
  
  #ifdef __BIG_ENDIAN_BITFIELD
  #define PKT_VLAN_PRESENT_BIT	7
  #else
  #define PKT_VLAN_PRESENT_BIT	0
  #endif
  #define PKT_VLAN_PRESENT_OFFSET()	offsetof(struct sk_buff, __pkt_vlan_present_offset)
  	/* private: */
  	__u8			__pkt_vlan_present_offset[0];
  	/* public: */
  	__u8			vlan_present:1;
  	__u8			csum_complete_sw:1;
  	__u8			csum_level:2;
  	__u8			csum_not_inet:1;
  	__u8			dst_pending_confirm:1;
  #ifdef CONFIG_IPV6_NDISC_NODETYPE
  	__u8			ndisc_nodetype:2;
  #endif
  
  	__u8			ipvs_property:1;
  	__u8			inner_protocol_type:1;
  	__u8			remcsum_offload:1;
  #ifdef CONFIG_NET_SWITCHDEV
  	__u8			offload_fwd_mark:1;
  	__u8			offload_l3_fwd_mark:1;
  #endif
  #ifdef CONFIG_NET_CLS_ACT
  	__u8			tc_skip_classify:1;
  	__u8			tc_at_ingress:1;
  #endif
  #ifdef CONFIG_NET_REDIRECT
  	__u8			redirected:1;
  	__u8			from_ingress:1;
  #endif
  #ifdef CONFIG_TLS_DEVICE
  	__u8			decrypted:1;
  #endif
  
  #ifdef CONFIG_NET_SCHED
  	__u16			tc_index;	/* traffic control index */
  #endif
  
  	union {
  		__wsum		csum;
  		struct {
  			__u16	csum_start;
  			__u16	csum_offset;
  		};
  	};
  	__u32			priority;
  	int			skb_iif;
  	__u32			hash;
  	__be16			vlan_proto;
  	__u16			vlan_tci;
  #if defined(CONFIG_NET_RX_BUSY_POLL) || defined(CONFIG_XPS)
  	union {
  		unsigned int	napi_id;
  		unsigned int	sender_cpu;
  	};
  #endif
  #ifdef CONFIG_NETWORK_SECMARK
  	__u32		secmark;
  #endif
  
  	union {
  		__u32		mark;
  		__u32		reserved_tailroom;
  	};
  
  	union {
  		__be16		inner_protocol;
  		__u8		inner_ipproto;
  	};
  
  	__u16			inner_transport_header;
  	__u16			inner_network_header;
  	__u16			inner_mac_header;
  
  	__be16			protocol;
  	__u16			transport_header;
  	__u16			network_header;
  	__u16			mac_header;
  
  	/* private: */
  	__u32			headers_end[0];
  	/* public: */
  
  	/* These elements must be at the end, see alloc_skb() for details.  */
  	sk_buff_data_t		tail;
  	sk_buff_data_t		end;
  	unsigned char		*head,
  				*data;
  	unsigned int		truesize;
  	refcount_t		users;
  
  #ifdef CONFIG_SKB_EXTENSIONS
  	/* only useable after checking ->active_extensions != 0 */
  	struct skb_ext		*extensions;
  #endif
  };
  
  #ifdef __KERNEL__
  /*
   *	Handling routines are only of interest to the kernel
   */
  
  #define SKB_ALLOC_FCLONE	0x01
  #define SKB_ALLOC_RX		0x02
  #define SKB_ALLOC_NAPI		0x04
  
  /**
   * skb_pfmemalloc - Test if the skb was allocated from PFMEMALLOC reserves
   * @skb: buffer
   */
  static inline bool skb_pfmemalloc(const struct sk_buff *skb)
  {
  	return unlikely(skb->pfmemalloc);
  }
  
  /*
   * skb might have a dst pointer attached, refcounted or not.
   * _skb_refdst low order bit is set if refcount was _not_ taken
   */
  #define SKB_DST_NOREF	1UL
  #define SKB_DST_PTRMASK	~(SKB_DST_NOREF)
  
  /**
   * skb_dst - returns skb dst_entry
   * @skb: buffer
   *
   * Returns skb dst_entry, regardless of reference taken or not.
   */
  static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
  {
  	/* If refdst was not refcounted, check we still are in a
  	 * rcu_read_lock section
  	 */
  	WARN_ON((skb->_skb_refdst & SKB_DST_NOREF) &&
  		!rcu_read_lock_held() &&
  		!rcu_read_lock_bh_held());
  	return (struct dst_entry *)(skb->_skb_refdst & SKB_DST_PTRMASK);
  }
  
  /**
   * skb_dst_set - sets skb dst
   * @skb: buffer
   * @dst: dst entry
   *
   * Sets skb dst, assuming a reference was taken on dst and should
   * be released by skb_dst_drop()
   */
  static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
  {
  	skb->_skb_refdst = (unsigned long)dst;
  }
  
  /**
   * skb_dst_set_noref - sets skb dst, hopefully, without taking reference
   * @skb: buffer
   * @dst: dst entry
   *
   * Sets skb dst, assuming a reference was not taken on dst.
   * If dst entry is cached, we do not take reference and dst_release
   * will be avoided by refdst_drop. If dst entry is not cached, we take
   * reference, so that last dst_release can destroy the dst immediately.
   */
  static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
  {
  	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
  	skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
  }
  
  /**
   * skb_dst_is_noref - Test if skb dst isn't refcounted
   * @skb: buffer
   */
  static inline bool skb_dst_is_noref(const struct sk_buff *skb)
  {
  	return (skb->_skb_refdst & SKB_DST_NOREF) && skb_dst(skb);
  }
  
  /**
   * skb_rtable - Returns the skb &rtable
   * @skb: buffer
   */
  static inline struct rtable *skb_rtable(const struct sk_buff *skb)
  {
  	return (struct rtable *)skb_dst(skb);
  }
  
  /* For mangling skb->pkt_type from user space side from applications
   * such as nft, tc, etc, we only allow a conservative subset of
   * possible pkt_types to be set.
  */
  static inline bool skb_pkt_type_ok(u32 ptype)
  {
  	return ptype <= PACKET_OTHERHOST;
  }
  
  /**
   * skb_napi_id - Returns the skb's NAPI id
   * @skb: buffer
   */
  static inline unsigned int skb_napi_id(const struct sk_buff *skb)
  {
  #ifdef CONFIG_NET_RX_BUSY_POLL
  	return skb->napi_id;
  #else
  	return 0;
  #endif
  }
  
  /**
   * skb_unref - decrement the skb's reference count
   * @skb: buffer
   *
   * Returns true if we can free the skb.
   */
  static inline bool skb_unref(struct sk_buff *skb)
  {
  	if (unlikely(!skb))
  		return false;
  	if (likely(refcount_read(&skb->users) == 1))
  		smp_rmb();
  	else if (likely(!refcount_dec_and_test(&skb->users)))
  		return false;
  
  	return true;
  }
  
  void skb_release_head_state(struct sk_buff *skb);
  void kfree_skb(struct sk_buff *skb);
  void kfree_skb_list(struct sk_buff *segs);
  void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt);
  void skb_tx_error(struct sk_buff *skb);
  
  #ifdef CONFIG_TRACEPOINTS
  void consume_skb(struct sk_buff *skb);
  #else
  static inline void consume_skb(struct sk_buff *skb)
  {
  	return kfree_skb(skb);
  }
  #endif
  
  void __consume_stateless_skb(struct sk_buff *skb);
  void  __kfree_skb(struct sk_buff *skb);
  extern struct kmem_cache *skbuff_head_cache;
  
  void kfree_skb_partial(struct sk_buff *skb, bool head_stolen);
  bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
  		      bool *fragstolen, int *delta_truesize);
  
  struct sk_buff *__alloc_skb(unsigned int size, gfp_t priority, int flags,
  			    int node);
  struct sk_buff *__build_skb(void *data, unsigned int frag_size);
  struct sk_buff *build_skb(void *data, unsigned int frag_size);
  struct sk_buff *build_skb_around(struct sk_buff *skb,
  				 void *data, unsigned int frag_size);
  
  /**
   * alloc_skb - allocate a network buffer
   * @size: size to allocate
   * @priority: allocation mask
   *
   * This function is a convenient wrapper around __alloc_skb().
   */
  static inline struct sk_buff *alloc_skb(unsigned int size,
  					gfp_t priority)
  {
  	return __alloc_skb(size, priority, 0, NUMA_NO_NODE);
  }
  
  struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
  				     unsigned long data_len,
  				     int max_page_order,
  				     int *errcode,
  				     gfp_t gfp_mask);
  struct sk_buff *alloc_skb_for_msg(struct sk_buff *first);
  
  /* Layout of fast clones : [skb1][skb2][fclone_ref] */
  struct sk_buff_fclones {
  	struct sk_buff	skb1;
  
  	struct sk_buff	skb2;
  
  	refcount_t	fclone_ref;
  };
  
  /**
   *	skb_fclone_busy - check if fclone is busy
   *	@sk: socket
   *	@skb: buffer
   *
   * Returns true if skb is a fast clone, and its clone is not freed.
   * Some drivers call skb_orphan() in their ndo_start_xmit(),
   * so we also check that this didnt happen.
   */
  static inline bool skb_fclone_busy(const struct sock *sk,
  				   const struct sk_buff *skb)
  {
  	const struct sk_buff_fclones *fclones;
  
  	fclones = container_of(skb, struct sk_buff_fclones, skb1);
  
  	return skb->fclone == SKB_FCLONE_ORIG &&
  	       refcount_read(&fclones->fclone_ref) > 1 &&
  	       fclones->skb2.sk == sk;
  }
  
  /**
   * alloc_skb_fclone - allocate a network buffer from fclone cache
   * @size: size to allocate
   * @priority: allocation mask
   *
   * This function is a convenient wrapper around __alloc_skb().
   */
  static inline struct sk_buff *alloc_skb_fclone(unsigned int size,
  					       gfp_t priority)
  {
  	return __alloc_skb(size, priority, SKB_ALLOC_FCLONE, NUMA_NO_NODE);
  }
  
  struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src);
  void skb_headers_offset_update(struct sk_buff *skb, int off);
  int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask);
  struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t priority);
  void skb_copy_header(struct sk_buff *new, const struct sk_buff *old);
  struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t priority);
  struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
  				   gfp_t gfp_mask, bool fclone);
  static inline struct sk_buff *__pskb_copy(struct sk_buff *skb, int headroom,
  					  gfp_t gfp_mask)
  {
  	return __pskb_copy_fclone(skb, headroom, gfp_mask, false);
  }
  
  int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, gfp_t gfp_mask);
  struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
  				     unsigned int headroom);
  struct sk_buff *skb_copy_expand(const struct sk_buff *skb, int newheadroom,
  				int newtailroom, gfp_t priority);
  int __must_check skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
  				     int offset, int len);
  int __must_check skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg,
  			      int offset, int len);
  int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer);
  int __skb_pad(struct sk_buff *skb, int pad, bool free_on_error);
  
  /**
   *	skb_pad			-	zero pad the tail of an skb
   *	@skb: buffer to pad
   *	@pad: space to pad
   *
   *	Ensure that a buffer is followed by a padding area that is zero
   *	filled. Used by network drivers which may DMA or transfer data
   *	beyond the buffer end onto the wire.
   *
   *	May return error in out of memory cases. The skb is freed on error.
   */
  static inline int skb_pad(struct sk_buff *skb, int pad)
  {
  	return __skb_pad(skb, pad, true);
  }
  #define dev_kfree_skb(a)	consume_skb(a)
  
  int skb_append_pagefrags(struct sk_buff *skb, struct page *page,
  			 int offset, size_t size);
  
  struct skb_seq_state {
  	__u32		lower_offset;
  	__u32		upper_offset;
  	__u32		frag_idx;
  	__u32		stepped_offset;
  	struct sk_buff	*root_skb;
  	struct sk_buff	*cur_skb;
  	__u8		*frag_data;
  };
  
  void skb_prepare_seq_read(struct sk_buff *skb, unsigned int from,
  			  unsigned int to, struct skb_seq_state *st);
  unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
  			  struct skb_seq_state *st);
  void skb_abort_seq_read(struct skb_seq_state *st);
  
  unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
  			   unsigned int to, struct ts_config *config);
  
  /*
   * Packet hash types specify the type of hash in skb_set_hash.
   *
   * Hash types refer to the protocol layer addresses which are used to
   * construct a packet's hash. The hashes are used to differentiate or identify
   * flows of the protocol layer for the hash type. Hash types are either
   * layer-2 (L2), layer-3 (L3), or layer-4 (L4).
   *
   * Properties of hashes:
   *
   * 1) Two packets in different flows have different hash values
   * 2) Two packets in the same flow should have the same hash value
   *
   * A hash at a higher layer is considered to be more specific. A driver should
   * set the most specific hash possible.
   *
   * A driver cannot indicate a more specific hash than the layer at which a hash
   * was computed. For instance an L3 hash cannot be set as an L4 hash.
   *
   * A driver may indicate a hash level which is less specific than the
   * actual layer the hash was computed on. For instance, a hash computed
   * at L4 may be considered an L3 hash. This should only be done if the
   * driver can't unambiguously determine that the HW computed the hash at
   * the higher layer. Note that the "should" in the second property above
   * permits this.
   */
  enum pkt_hash_types {
  	PKT_HASH_TYPE_NONE,	/* Undefined type */
  	PKT_HASH_TYPE_L2,	/* Input: src_MAC, dest_MAC */
  	PKT_HASH_TYPE_L3,	/* Input: src_IP, dst_IP */
  	PKT_HASH_TYPE_L4,	/* Input: src_IP, dst_IP, src_port, dst_port */
  };
  
  static inline void skb_clear_hash(struct sk_buff *skb)
  {
  	skb->hash = 0;
  	skb->sw_hash = 0;
  	skb->l4_hash = 0;
  }
  
  static inline void skb_clear_hash_if_not_l4(struct sk_buff *skb)
  {
  	if (!skb->l4_hash)
  		skb_clear_hash(skb);
  }
  
  static inline void
  __skb_set_hash(struct sk_buff *skb, __u32 hash, bool is_sw, bool is_l4)
  {
  	skb->l4_hash = is_l4;
  	skb->sw_hash = is_sw;
  	skb->hash = hash;
  }
  
  static inline void
  skb_set_hash(struct sk_buff *skb, __u32 hash, enum pkt_hash_types type)
  {
  	/* Used by drivers to set hash from HW */
  	__skb_set_hash(skb, hash, false, type == PKT_HASH_TYPE_L4);
  }
  
  static inline void
  __skb_set_sw_hash(struct sk_buff *skb, __u32 hash, bool is_l4)
  {
  	__skb_set_hash(skb, hash, true, is_l4);
  }
  
  void __skb_get_hash(struct sk_buff *skb);
  u32 __skb_get_hash_symmetric(const struct sk_buff *skb);
  u32 skb_get_poff(const struct sk_buff *skb);
  u32 __skb_get_poff(const struct sk_buff *skb, void *data,
  		   const struct flow_keys_basic *keys, int hlen);
  __be32 __skb_flow_get_ports(const struct sk_buff *skb, int thoff, u8 ip_proto,
  			    void *data, int hlen_proto);
  
  static inline __be32 skb_flow_get_ports(const struct sk_buff *skb,
  					int thoff, u8 ip_proto)
  {
  	return __skb_flow_get_ports(skb, thoff, ip_proto, NULL, 0);
  }
  
  void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
  			     const struct flow_dissector_key *key,
  			     unsigned int key_count);
  
  struct bpf_flow_dissector;
  bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
  		      __be16 proto, int nhoff, int hlen, unsigned int flags);
  
  bool __skb_flow_dissect(const struct net *net,
  			const struct sk_buff *skb,
  			struct flow_dissector *flow_dissector,
  			void *target_container,
  			void *data, __be16 proto, int nhoff, int hlen,
  			unsigned int flags);
  
  static inline bool skb_flow_dissect(const struct sk_buff *skb,
  				    struct flow_dissector *flow_dissector,
  				    void *target_container, unsigned int flags)
  {
  	return __skb_flow_dissect(NULL, skb, flow_dissector,
  				  target_container, NULL, 0, 0, 0, flags);
  }
  
  static inline bool skb_flow_dissect_flow_keys(const struct sk_buff *skb,
  					      struct flow_keys *flow,
  					      unsigned int flags)
  {
  	memset(flow, 0, sizeof(*flow));
  	return __skb_flow_dissect(NULL, skb, &flow_keys_dissector,
  				  flow, NULL, 0, 0, 0, flags);
  }
  
  static inline bool
  skb_flow_dissect_flow_keys_basic(const struct net *net,
  				 const struct sk_buff *skb,
  				 struct flow_keys_basic *flow, void *data,
  				 __be16 proto, int nhoff, int hlen,
  				 unsigned int flags)
  {
  	memset(flow, 0, sizeof(*flow));
  	return __skb_flow_dissect(net, skb, &flow_keys_basic_dissector, flow,
  				  data, proto, nhoff, hlen, flags);
  }
  
  void skb_flow_dissect_meta(const struct sk_buff *skb,
  			   struct flow_dissector *flow_dissector,
  			   void *target_container);
  
  /* Gets a skb connection tracking info, ctinfo map should be a
   * map of mapsize to translate enum ip_conntrack_info states
   * to user states.
   */
  void
  skb_flow_dissect_ct(const struct sk_buff *skb,
  		    struct flow_dissector *flow_dissector,
  		    void *target_container,
  		    u16 *ctinfo_map,
  		    size_t mapsize);
  void
  skb_flow_dissect_tunnel_info(const struct sk_buff *skb,
  			     struct flow_dissector *flow_dissector,
  			     void *target_container);
  
  void skb_flow_dissect_hash(const struct sk_buff *skb,
  			   struct flow_dissector *flow_dissector,
  			   void *target_container);
  
  static inline __u32 skb_get_hash(struct sk_buff *skb)
  {
  	if (!skb->l4_hash && !skb->sw_hash)
  		__skb_get_hash(skb);
  
  	return skb->hash;
  }
  
  static inline __u32 skb_get_hash_flowi6(struct sk_buff *skb, const struct flowi6 *fl6)
  {
  	if (!skb->l4_hash && !skb->sw_hash) {
  		struct flow_keys keys;
  		__u32 hash = __get_hash_from_flowi6(fl6, &keys);
  
  		__skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
  	}
  
  	return skb->hash;
  }
  
  __u32 skb_get_hash_perturb(const struct sk_buff *skb,
  			   const siphash_key_t *perturb);
  
  static inline __u32 skb_get_hash_raw(const struct sk_buff *skb)
  {
  	return skb->hash;
  }
  
  static inline void skb_copy_hash(struct sk_buff *to, const struct sk_buff *from)
  {
  	to->hash = from->hash;
  	to->sw_hash = from->sw_hash;
  	to->l4_hash = from->l4_hash;
  };
  
  static inline void skb_copy_decrypted(struct sk_buff *to,
  				      const struct sk_buff *from)
  {
  #ifdef CONFIG_TLS_DEVICE
  	to->decrypted = from->decrypted;
  #endif
  }
  
  #ifdef NET_SKBUFF_DATA_USES_OFFSET
  static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
  {
  	return skb->head + skb->end;
  }
  
  static inline unsigned int skb_end_offset(const struct sk_buff *skb)
  {
  	return skb->end;
  }
  #else
  static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
  {
  	return skb->end;
  }
  
  static inline unsigned int skb_end_offset(const struct sk_buff *skb)
  {
  	return skb->end - skb->head;
  }
  #endif
  
  /* Internal */
  #define skb_shinfo(SKB)	((struct skb_shared_info *)(skb_end_pointer(SKB)))
  
  static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
  {
  	return &skb_shinfo(skb)->hwtstamps;
  }
  
  static inline struct ubuf_info *skb_zcopy(struct sk_buff *skb)
  {
  	bool is_zcopy = skb && skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY;
  
  	return is_zcopy ? skb_uarg(skb) : NULL;
  }
  
  static inline void skb_zcopy_set(struct sk_buff *skb, struct ubuf_info *uarg,
  				 bool *have_ref)
  {
  	if (skb && uarg && !skb_zcopy(skb)) {
  		if (unlikely(have_ref && *have_ref))
  			*have_ref = false;
  		else
  			sock_zerocopy_get(uarg);
  		skb_shinfo(skb)->destructor_arg = uarg;
  		skb_shinfo(skb)->tx_flags |= SKBTX_ZEROCOPY_FRAG;
  	}
  }
  
  static inline void skb_zcopy_set_nouarg(struct sk_buff *skb, void *val)
  {
  	skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t) val | 0x1UL);
  	skb_shinfo(skb)->tx_flags |= SKBTX_ZEROCOPY_FRAG;
  }
  
  static inline bool skb_zcopy_is_nouarg(struct sk_buff *skb)
  {
  	return (uintptr_t) skb_shinfo(skb)->destructor_arg & 0x1UL;
  }
  
  static inline void *skb_zcopy_get_nouarg(struct sk_buff *skb)
  {
  	return (void *)((uintptr_t) skb_shinfo(skb)->destructor_arg & ~0x1UL);
  }
  
  /* Release a reference on a zerocopy structure */
  static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
  {
  	struct ubuf_info *uarg = skb_zcopy(skb);
  
  	if (uarg) {
  		if (skb_zcopy_is_nouarg(skb)) {
  			/* no notification callback */
  		} else if (uarg->callback == sock_zerocopy_callback) {
  			uarg->zerocopy = uarg->zerocopy && zerocopy;
  			sock_zerocopy_put(uarg);
  		} else {
  			uarg->callback(uarg, zerocopy);
  		}
  
  		skb_shinfo(skb)->tx_flags &= ~SKBTX_ZEROCOPY_FRAG;
  	}
  }
  
  /* Abort a zerocopy operation and revert zckey on error in send syscall */
  static inline void skb_zcopy_abort(struct sk_buff *skb)
  {
  	struct ubuf_info *uarg = skb_zcopy(skb);
  
  	if (uarg) {
  		sock_zerocopy_put_abort(uarg, false);
  		skb_shinfo(skb)->tx_flags &= ~SKBTX_ZEROCOPY_FRAG;
  	}
  }
  
  static inline void skb_mark_not_on_list(struct sk_buff *skb)
  {
  	skb->next = NULL;
  }
  
  /* Iterate through singly-linked GSO fragments of an skb. */
  #define skb_list_walk_safe(first, skb, next_skb)                               \
  	for ((skb) = (first), (next_skb) = (skb) ? (skb)->next : NULL; (skb);  \
  	     (skb) = (next_skb), (next_skb) = (skb) ? (skb)->next : NULL)
  
  static inline void skb_list_del_init(struct sk_buff *skb)
  {
  	__list_del_entry(&skb->list);
  	skb_mark_not_on_list(skb);
  }
  
  /**
   *	skb_queue_empty - check if a queue is empty
   *	@list: queue head
   *
   *	Returns true if the queue is empty, false otherwise.
   */
  static inline int skb_queue_empty(const struct sk_buff_head *list)
  {
  	return list->next == (const struct sk_buff *) list;
  }
  
  /**
   *	skb_queue_empty_lockless - check if a queue is empty
   *	@list: queue head
   *
   *	Returns true if the queue is empty, false otherwise.
   *	This variant can be used in lockless contexts.
   */
  static inline bool skb_queue_empty_lockless(const struct sk_buff_head *list)
  {
  	return READ_ONCE(list->next) == (const struct sk_buff *) list;
  }
  
  
  /**
   *	skb_queue_is_last - check if skb is the last entry in the queue
   *	@list: queue head
   *	@skb: buffer
   *
   *	Returns true if @skb is the last buffer on the list.
   */
  static inline bool skb_queue_is_last(const struct sk_buff_head *list,
  				     const struct sk_buff *skb)
  {
  	return skb->next == (const struct sk_buff *) list;
  }
  
  /**
   *	skb_queue_is_first - check if skb is the first entry in the queue
   *	@list: queue head
   *	@skb: buffer
   *
   *	Returns true if @skb is the first buffer on the list.
   */
  static inline bool skb_queue_is_first(const struct sk_buff_head *list,
  				      const struct sk_buff *skb)
  {
  	return skb->prev == (const struct sk_buff *) list;
  }
  
  /**
   *	skb_queue_next - return the next packet in the queue
   *	@list: queue head
   *	@skb: current buffer
   *
   *	Return the next packet in @list after @skb.  It is only valid to
   *	call this if skb_queue_is_last() evaluates to false.
   */
  static inline struct sk_buff *skb_queue_next(const struct sk_buff_head *list,
  					     const struct sk_buff *skb)
  {
  	/* This BUG_ON may seem severe, but if we just return then we
  	 * are going to dereference garbage.
  	 */
  	BUG_ON(skb_queue_is_last(list, skb));
  	return skb->next;
  }
  
  /**
   *	skb_queue_prev - return the prev packet in the queue
   *	@list: queue head
   *	@skb: current buffer
   *
   *	Return the prev packet in @list before @skb.  It is only valid to
   *	call this if skb_queue_is_first() evaluates to false.
   */
  static inline struct sk_buff *skb_queue_prev(const struct sk_buff_head *list,
  					     const struct sk_buff *skb)
  {
  	/* This BUG_ON may seem severe, but if we just return then we
  	 * are going to dereference garbage.
  	 */
  	BUG_ON(skb_queue_is_first(list, skb));
  	return skb->prev;
  }
  
  /**
   *	skb_get - reference buffer
   *	@skb: buffer to reference
   *
   *	Makes another reference to a socket buffer and returns a pointer
   *	to the buffer.
   */
  static inline struct sk_buff *skb_get(struct sk_buff *skb)
  {
  	refcount_inc(&skb->users);
  	return skb;
  }
  
  /*
   * If users == 1, we are the only owner and can avoid redundant atomic changes.
   */
  
  /**
   *	skb_cloned - is the buffer a clone
   *	@skb: buffer to check
   *
   *	Returns true if the buffer was generated with skb_clone() and is
   *	one of multiple shared copies of the buffer. Cloned buffers are
   *	shared data so must not be written to under normal circumstances.
   */
  static inline int skb_cloned(const struct sk_buff *skb)
  {
  	return skb->cloned &&
  	       (atomic_read(&skb_shinfo(skb)->dataref) & SKB_DATAREF_MASK) != 1;
  }
  
  static inline int skb_unclone(struct sk_buff *skb, gfp_t pri)
  {
  	might_sleep_if(gfpflags_allow_blocking(pri));
  
  	if (skb_cloned(skb))
  		return pskb_expand_head(skb, 0, 0, pri);
  
  	return 0;
  }
  
  /**
   *	skb_header_cloned - is the header a clone
   *	@skb: buffer to check
   *
   *	Returns true if modifying the header part of the buffer requires
   *	the data to be copied.
   */
  static inline int skb_header_cloned(const struct sk_buff *skb)
  {
  	int dataref;
  
  	if (!skb->cloned)
  		return 0;
  
  	dataref = atomic_read(&skb_shinfo(skb)->dataref);
  	dataref = (dataref & SKB_DATAREF_MASK) - (dataref >> SKB_DATAREF_SHIFT);
  	return dataref != 1;
  }
  
  static inline int skb_header_unclone(struct sk_buff *skb, gfp_t pri)
  {
  	might_sleep_if(gfpflags_allow_blocking(pri));
  
  	if (skb_header_cloned(skb))
  		return pskb_expand_head(skb, 0, 0, pri);
  
  	return 0;
  }
  
  /**
   *	__skb_header_release - release reference to header
   *	@skb: buffer to operate on
   */
  static inline void __skb_header_release(struct sk_buff *skb)
  {
  	skb->nohdr = 1;
  	atomic_set(&skb_shinfo(skb)->dataref, 1 + (1 << SKB_DATAREF_SHIFT));
  }
  
  
  /**
   *	skb_shared - is the buffer shared
   *	@skb: buffer to check
   *
   *	Returns true if more than one person has a reference to this
   *	buffer.
   */
  static inline int skb_shared(const struct sk_buff *skb)
  {
  	return refcount_read(&skb->users) != 1;
  }
  
  /**
   *	skb_share_check - check if buffer is shared and if so clone it
   *	@skb: buffer to check
   *	@pri: priority for memory allocation
   *
   *	If the buffer is shared the buffer is cloned and the old copy
   *	drops a reference. A new clone with a single reference is returned.
   *	If the buffer is not shared the original buffer is returned. When
   *	being called from interrupt status or with spinlocks held pri must
   *	be GFP_ATOMIC.
   *
   *	NULL is returned on a memory allocation failure.
   */
  static inline struct sk_buff *skb_share_check(struct sk_buff *skb, gfp_t pri)
  {
  	might_sleep_if(gfpflags_allow_blocking(pri));
  	if (skb_shared(skb)) {
  		struct sk_buff *nskb = skb_clone(skb, pri);
  
  		if (likely(nskb))
  			consume_skb(skb);
  		else
  			kfree_skb(skb);
  		skb = nskb;
  	}
  	return skb;
  }
  
  /*
   *	Copy shared buffers into a new sk_buff. We effectively do COW on
   *	packets to handle cases where we have a local reader and forward
   *	and a couple of other messy ones. The normal one is tcpdumping
   *	a packet thats being forwarded.
   */
  
  /**
   *	skb_unshare - make a copy of a shared buffer
   *	@skb: buffer to check
   *	@pri: priority for memory allocation
   *
   *	If the socket buffer is a clone then this function creates a new
   *	copy of the data, drops a reference count on the old copy and returns
   *	the new copy with the reference count at 1. If the buffer is not a clone
   *	the original buffer is returned. When called with a spinlock held or
   *	from interrupt state @pri must be %GFP_ATOMIC
   *
   *	%NULL is returned on a memory allocation failure.
   */
  static inline struct sk_buff *skb_unshare(struct sk_buff *skb,
  					  gfp_t pri)
  {
  	might_sleep_if(gfpflags_allow_blocking(pri));
  	if (skb_cloned(skb)) {
  		struct sk_buff *nskb = skb_copy(skb, pri);
  
  		/* Free our shared copy */
  		if (likely(nskb))
  			consume_skb(skb);
  		else
  			kfree_skb(skb);
  		skb = nskb;
  	}
  	return skb;
  }
  
  /**
   *	skb_peek - peek at the head of an &sk_buff_head
   *	@list_: list to peek at
   *
   *	Peek an &sk_buff. Unlike most other operations you _MUST_
   *	be careful with this one. A peek leaves the buffer on the
   *	list and someone else may run off with it. You must hold
   *	the appropriate locks or have a private queue to do this.
   *
   *	Returns %NULL for an empty list or a pointer to the head element.
   *	The reference count is not incremented and the reference is therefore
   *	volatile. Use with caution.
   */
  static inline struct sk_buff *skb_peek(const struct sk_buff_head *list_)
  {
  	struct sk_buff *skb = list_->next;
  
  	if (skb == (struct sk_buff *)list_)
  		skb = NULL;
  	return skb;
  }
  
  /**
   *	__skb_peek - peek at the head of a non-empty &sk_buff_head
   *	@list_: list to peek at
   *
   *	Like skb_peek(), but the caller knows that the list is not empty.
   */
  static inline struct sk_buff *__skb_peek(const struct sk_buff_head *list_)
  {
  	return list_->next;
  }
  
  /**
   *	skb_peek_next - peek skb following the given one from a queue
   *	@skb: skb to start from
   *	@list_: list to peek at
   *
   *	Returns %NULL when the end of the list is met or a pointer to the
   *	next element. The reference count is not incremented and the
   *	reference is therefore volatile. Use with caution.
   */
  static inline struct sk_buff *skb_peek_next(struct sk_buff *skb,
  		const struct sk_buff_head *list_)
  {
  	struct sk_buff *next = skb->next;
  
  	if (next == (struct sk_buff *)list_)
  		next = NULL;
  	return next;
  }
  
  /**
   *	skb_peek_tail - peek at the tail of an &sk_buff_head
   *	@list_: list to peek at
   *
   *	Peek an &sk_buff. Unlike most other operations you _MUST_
   *	be careful with this one. A peek leaves the buffer on the
   *	list and someone else may run off with it. You must hold
   *	the appropriate locks or have a private queue to do this.
   *
   *	Returns %NULL for an empty list or a pointer to the tail element.
   *	The reference count is not incremented and the reference is therefore
   *	volatile. Use with caution.
   */
  static inline struct sk_buff *skb_peek_tail(const struct sk_buff_head *list_)
  {
  	struct sk_buff *skb = READ_ONCE(list_->prev);
  
  	if (skb == (struct sk_buff *)list_)
  		skb = NULL;
  	return skb;
  
  }
  
  /**
   *	skb_queue_len	- get queue length
   *	@list_: list to measure
   *
   *	Return the length of an &sk_buff queue.
   */
  static inline __u32 skb_queue_len(const struct sk_buff_head *list_)
  {
  	return list_->qlen;
  }
  
  /**
   *	skb_queue_len_lockless	- get queue length
   *	@list_: list to measure
   *
   *	Return the length of an &sk_buff queue.
   *	This variant can be used in lockless contexts.
   */
  static inline __u32 skb_queue_len_lockless(const struct sk_buff_head *list_)
  {
  	return READ_ONCE(list_->qlen);
  }
  
  /**
   *	__skb_queue_head_init - initialize non-spinlock portions of sk_buff_head
   *	@list: queue to initialize
   *
   *	This initializes only the list and queue length aspects of
   *	an sk_buff_head object.  This allows to initialize the list
   *	aspects of an sk_buff_head without reinitializing things like
   *	the spinlock.  It can also be used for on-stack sk_buff_head
   *	objects where the spinlock is known to not be used.
   */
  static inline void __skb_queue_head_init(struct sk_buff_head *list)
  {
  	list->prev = list->next = (struct sk_buff *)list;
  	list->qlen = 0;
  }
  
  /*
   * This function creates a split out lock class for each invocation;
   * this is needed for now since a whole lot of users of the skb-queue
   * infrastructure in drivers have different locking usage (in hardirq)
   * than the networking core (in softirq only). In the long run either the
   * network layer or drivers should need annotation to consolidate the
   * main types of usage into 3 classes.
   */
  static inline void skb_queue_head_init(struct sk_buff_head *list)
  {
  	spin_lock_init(&list->lock);
  	__skb_queue_head_init(list);
  }
  
  static inline void skb_queue_head_init_class(struct sk_buff_head *list,
  		struct lock_class_key *class)
  {
  	skb_queue_head_init(list);
  	lockdep_set_class(&list->lock, class);
  }
  
  /*
   *	Insert an sk_buff on a list.
   *
   *	The "__skb_xxxx()" functions are the non-atomic ones that
   *	can only be called with interrupts disabled.
   */
  static inline void __skb_insert(struct sk_buff *newsk,
  				struct sk_buff *prev, struct sk_buff *next,
  				struct sk_buff_head *list)
  {
  	/* See skb_queue_empty_lockless() and skb_peek_tail()
  	 * for the opposite READ_ONCE()
  	 */
  	WRITE_ONCE(newsk->next, next);
  	WRITE_ONCE(newsk->prev, prev);
  	WRITE_ONCE(next->prev, newsk);
  	WRITE_ONCE(prev->next, newsk);
  	list->qlen++;
  }
  
  static inline void __skb_queue_splice(const struct sk_buff_head *list,
  				      struct sk_buff *prev,
  				      struct sk_buff *next)
  {
  	struct sk_buff *first = list->next;
  	struct sk_buff *last = list->prev;
  
  	WRITE_ONCE(first->prev, prev);
  	WRITE_ONCE(prev->next, first);
  
  	WRITE_ONCE(last->next, next);
  	WRITE_ONCE(next->prev, last);
  }
  
  /**
   *	skb_queue_splice - join two skb lists, this is designed for stacks
   *	@list: the new list to add
   *	@head: the place to add it in the first list
   */
  static inline void skb_queue_splice(const struct sk_buff_head *list,
  				    struct sk_buff_head *head)
  {
  	if (!skb_queue_empty(list)) {
  		__skb_queue_splice(list, (struct sk_buff *) head, head->next);
  		head->qlen += list->qlen;
  	}
  }
  
  /**
   *	skb_queue_splice_init - join two skb lists and reinitialise the emptied list
   *	@list: the new list to add
   *	@head: the place to add it in the first list
   *
   *	The list at @list is reinitialised
   */
  static inline void skb_queue_splice_init(struct sk_buff_head *list,
  					 struct sk_buff_head *head)
  {
  	if (!skb_queue_empty(list)) {
  		__skb_queue_splice(list, (struct sk_buff *) head, head->next);
  		head->qlen += list->qlen;
  		__skb_queue_head_init(list);
  	}
  }
  
  /**
   *	skb_queue_splice_tail - join two skb lists, each list being a queue
   *	@list: the new list to add
   *	@head: the place to add it in the first list
   */
  static inline void skb_queue_splice_tail(const struct sk_buff_head *list,
  					 struct sk_buff_head *head)
  {
  	if (!skb_queue_empty(list)) {
  		__skb_queue_splice(list, head->prev, (struct sk_buff *) head);
  		head->qlen += list->qlen;
  	}
  }
  
  /**
   *	skb_queue_splice_tail_init - join two skb lists and reinitialise the emptied list
   *	@list: the new list to add
   *	@head: the place to add it in the first list
   *
   *	Each of the lists is a queue.
   *	The list at @list is reinitialised
   */
  static inline void skb_queue_splice_tail_init(struct sk_buff_head *list,
  					      struct sk_buff_head *head)
  {
  	if (!skb_queue_empty(list)) {
  		__skb_queue_splice(list, head->prev, (struct sk_buff *) head);
  		head->qlen += list->qlen;
  		__skb_queue_head_init(list);
  	}
  }
  
  /**
   *	__skb_queue_after - queue a buffer at the list head
   *	@list: list to use
   *	@prev: place after this buffer
   *	@newsk: buffer to queue
   *
   *	Queue a buffer int the middle of a list. This function takes no locks
   *	and you must therefore hold required locks before calling it.
   *
   *	A buffer cannot be placed on two lists at the same time.
   */
  static inline void __skb_queue_after(struct sk_buff_head *list,
  				     struct sk_buff *prev,
  				     struct sk_buff *newsk)
  {
  	__skb_insert(newsk, prev, prev->next, list);
  }
  
  void skb_append(struct sk_buff *old, struct sk_buff *newsk,
  		struct sk_buff_head *list);
  
  static inline void __skb_queue_before(struct sk_buff_head *list,
  				      struct sk_buff *next,
  				      struct sk_buff *newsk)
  {
  	__skb_insert(newsk, next->prev, next, list);
  }
  
  /**
   *	__skb_queue_head - queue a buffer at the list head
   *	@list: list to use
   *	@newsk: buffer to queue
   *
   *	Queue a buffer at the start of a list. This function takes no locks
   *	and you must therefore hold required locks before calling it.
   *
   *	A buffer cannot be placed on two lists at the same time.
   */
  static inline void __skb_queue_head(struct sk_buff_head *list,
  				    struct sk_buff *newsk)
  {
  	__skb_queue_after(list, (struct sk_buff *)list, newsk);
  }
  void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk);
  
  /**
   *	__skb_queue_tail - queue a buffer at the list tail
   *	@list: list to use
   *	@newsk: buffer to queue
   *
   *	Queue a buffer at the end of a list. This function takes no locks
   *	and you must therefore hold required locks before calling it.
   *
   *	A buffer cannot be placed on two lists at the same time.
   */
  static inline void __skb_queue_tail(struct sk_buff_head *list,
  				   struct sk_buff *newsk)
  {
  	__skb_queue_before(list, (struct sk_buff *)list, newsk);
  }
  void skb_queue_tail(struct sk_buff_head *list, struct sk_buff *newsk);
  
  /*
   * remove sk_buff from list. _Must_ be called atomically, and with
   * the list known..
   */
  void skb_unlink(struct sk_buff *skb, struct sk_buff_head *list);
  static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list)
  {
  	struct sk_buff *next, *prev;
  
  	WRITE_ONCE(list->qlen, list->qlen - 1);
  	next	   = skb->next;
  	prev	   = skb->prev;
  	skb->next  = skb->prev = NULL;
  	WRITE_ONCE(next->prev, prev);
  	WRITE_ONCE(prev->next, next);
  }
  
  /**
   *	__skb_dequeue - remove from the head of the queue
   *	@list: list to dequeue from
   *
   *	Remove the head of the list. This function does not take any locks
   *	so must be used with appropriate locks held only. The head item is
   *	returned or %NULL if the list is empty.
   */
  static inline struct sk_buff *__skb_dequeue(struct sk_buff_head *list)
  {
  	struct sk_buff *skb = skb_peek(list);
  	if (skb)
  		__skb_unlink(skb, list);
  	return skb;
  }
  struct sk_buff *skb_dequeue(struct sk_buff_head *list);
  
  /**
   *	__skb_dequeue_tail - remove from the tail of the queue
   *	@list: list to dequeue from
   *
   *	Remove the tail of the list. This function does not take any locks
   *	so must be used with appropriate locks held only. The tail item is
   *	returned or %NULL if the list is empty.
   */
  static inline struct sk_buff *__skb_dequeue_tail(struct sk_buff_head *list)
  {
  	struct sk_buff *skb = skb_peek_tail(list);
  	if (skb)
  		__skb_unlink(skb, list);
  	return skb;
  }
  struct sk_buff *skb_dequeue_tail(struct sk_buff_head *list);
  
  
  static inline bool skb_is_nonlinear(const struct sk_buff *skb)
  {
  	return skb->data_len;
  }
  
  static inline unsigned int skb_headlen(const struct sk_buff *skb)
  {
  	return skb->len - skb->data_len;
  }
  
  static inline unsigned int __skb_pagelen(const struct sk_buff *skb)
  {
  	unsigned int i, len = 0;
  
  	for (i = skb_shinfo(skb)->nr_frags - 1; (int)i >= 0; i--)
  		len += skb_frag_size(&skb_shinfo(skb)->frags[i]);
  	return len;
  }
  
  static inline unsigned int skb_pagelen(const struct sk_buff *skb)
  {
  	return skb_headlen(skb) + __skb_pagelen(skb);
  }
  
  /**
   * __skb_fill_page_desc - initialise a paged fragment in an skb
   * @skb: buffer containing fragment to be initialised
   * @i: paged fragment index to initialise
   * @page: the page to use for this fragment
   * @off: the offset to the data with @page
   * @size: the length of the data
   *
   * Initialises the @i'th fragment of @skb to point to &size bytes at
   * offset @off within @page.
   *
   * Does not take any additional reference on the fragment.
   */
  static inline void __skb_fill_page_desc(struct sk_buff *skb, int i,
  					struct page *page, int off, int size)
  {
  	skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  
  	/*
  	 * Propagate page pfmemalloc to the skb if we can. The problem is
  	 * that not all callers have unique ownership of the page but rely
  	 * on page_is_pfmemalloc doing the right thing(tm).
  	 */
  	frag->bv_page		  = page;
  	frag->bv_offset		  = off;
  	skb_frag_size_set(frag, size);
  
  	page = compound_head(page);
  	if (page_is_pfmemalloc(page))
  		skb->pfmemalloc	= true;
  }
  
  /**
   * skb_fill_page_desc - initialise a paged fragment in an skb
   * @skb: buffer containing fragment to be initialised
   * @i: paged fragment index to initialise
   * @page: the page to use for this fragment
   * @off: the offset to the data with @page
   * @size: the length of the data
   *
   * As per __skb_fill_page_desc() -- initialises the @i'th fragment of
   * @skb to point to @size bytes at offset @off within @page. In
   * addition updates @skb such that @i is the last fragment.
   *
   * Does not take any additional reference on the fragment.
   */
  static inline void skb_fill_page_desc(struct sk_buff *skb, int i,
  				      struct page *page, int off, int size)
  {
  	__skb_fill_page_desc(skb, i, page, off, size);
  	skb_shinfo(skb)->nr_frags = i + 1;
  }
  
  void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int off,
  		     int size, unsigned int truesize);
  
  void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
  			  unsigned int truesize);
  
  #define SKB_LINEAR_ASSERT(skb)  BUG_ON(skb_is_nonlinear(skb))
  
  #ifdef NET_SKBUFF_DATA_USES_OFFSET
  static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
  {
  	return skb->head + skb->tail;
  }
  
  static inline void skb_reset_tail_pointer(struct sk_buff *skb)
  {
  	skb->tail = skb->data - skb->head;
  }
  
  static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
  {
  	skb_reset_tail_pointer(skb);
  	skb->tail += offset;
  }
  
  #else /* NET_SKBUFF_DATA_USES_OFFSET */
  static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
  {
  	return skb->tail;
  }
  
  static inline void skb_reset_tail_pointer(struct sk_buff *skb)
  {
  	skb->tail = skb->data;
  }
  
  static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset)
  {
  	skb->tail = skb->data + offset;
  }
  
  #endif /* NET_SKBUFF_DATA_USES_OFFSET */
  
  /*
   *	Add data to an sk_buff
   */
  void *pskb_put(struct sk_buff *skb, struct sk_buff *tail, int len);
  void *skb_put(struct sk_buff *skb, unsigned int len);
  static inline void *__skb_put(struct sk_buff *skb, unsigned int len)
  {
  	void *tmp = skb_tail_pointer(skb);
  	SKB_LINEAR_ASSERT(skb);
  	skb->tail += len;
  	skb->len  += len;
  	return tmp;
  }
  
  static inline void *__skb_put_zero(struct sk_buff *skb, unsigned int len)
  {
  	void *tmp = __skb_put(skb, len);
  
  	memset(tmp, 0, len);
  	return tmp;
  }
  
  static inline void *__skb_put_data(struct sk_buff *skb, const void *data,
  				   unsigned int len)
  {
  	void *tmp = __skb_put(skb, len);
  
  	memcpy(tmp, data, len);
  	return tmp;
  }
  
  static inline void __skb_put_u8(struct sk_buff *skb, u8 val)
  {
  	*(u8 *)__skb_put(skb, 1) = val;
  }
  
  static inline void *skb_put_zero(struct sk_buff *skb, unsigned int len)
  {
  	void *tmp = skb_put(skb, len);
  
  	memset(tmp, 0, len);
  
  	return tmp;
  }
  
  static inline void *skb_put_data(struct sk_buff *skb, const void *data,
  				 unsigned int len)
  {
  	void *tmp = skb_put(skb, len);
  
  	memcpy(tmp, data, len);
  
  	return tmp;
  }
  
  static inline void skb_put_u8(struct sk_buff *skb, u8 val)
  {
  	*(u8 *)skb_put(skb, 1) = val;
  }
  
  void *skb_push(struct sk_buff *skb, unsigned int len);
  static inline void *__skb_push(struct sk_buff *skb, unsigned int len)
  {
  	skb->data -= len;
  	skb->len  += len;
  	return skb->data;
  }
  
  void *skb_pull(struct sk_buff *skb, unsigned int len);
  static inline void *__skb_pull(struct sk_buff *skb, unsigned int len)
  {
  	skb->len -= len;
  	BUG_ON(skb->len < skb->data_len);
  	return skb->data += len;
  }
  
  static inline void *skb_pull_inline(struct sk_buff *skb, unsigned int len)
  {
  	return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
  }
  
  void *__pskb_pull_tail(struct sk_buff *skb, int delta);
  
  static inline void *__pskb_pull(struct sk_buff *skb, unsigned int len)
  {
  	if (len > skb_headlen(skb) &&
  	    !__pskb_pull_tail(skb, len - skb_headlen(skb)))
  		return NULL;
  	skb->len -= len;
  	return skb->data += len;
  }
  
  static inline void *pskb_pull(struct sk_buff *skb, unsigned int len)
  {
  	return unlikely(len > skb->len) ? NULL : __pskb_pull(skb, len);
  }
  
  static inline bool pskb_may_pull(struct sk_buff *skb, unsigned int len)
  {
  	if (likely(len <= skb_headlen(skb)))
  		return true;
  	if (unlikely(len > skb->len))
  		return false;
  	return __pskb_pull_tail(skb, len - skb_headlen(skb)) != NULL;
  }
  
  void skb_condense(struct sk_buff *skb);
  
  /**
   *	skb_headroom - bytes at buffer head
   *	@skb: buffer to check
   *
   *	Return the number of bytes of free space at the head of an &sk_buff.
   */
  static inline unsigned int skb_headroom(const struct sk_buff *skb)
  {
  	return skb->data - skb->head;
  }
  
  /**
   *	skb_tailroom - bytes at buffer end
   *	@skb: buffer to check
   *
   *	Return the number of bytes of free space at the tail of an sk_buff
   */
  static inline int skb_tailroom(const struct sk_buff *skb)
  {
  	return skb_is_nonlinear(skb) ? 0 : skb->end - skb->tail;
  }
  
  /**
   *	skb_availroom - bytes at buffer end
   *	@skb: buffer to check
   *
   *	Return the number of bytes of free space at the tail of an sk_buff
   *	allocated by sk_stream_alloc()
   */
  static inline int skb_availroom(const struct sk_buff *skb)
  {
  	if (skb_is_nonlinear(skb))
  		return 0;
  
  	return skb->end - skb->tail - skb->reserved_tailroom;
  }
  
  /**
   *	skb_reserve - adjust headroom
   *	@skb: buffer to alter
   *	@len: bytes to move
   *
   *	Increase the headroom of an empty &sk_buff by reducing the tail
   *	room. This is only allowed for an empty buffer.
   */
  static inline void skb_reserve(struct sk_buff *skb, int len)
  {
  	skb->data += len;
  	skb->tail += len;
  }
  
  /**
   *	skb_tailroom_reserve - adjust reserved_tailroom
   *	@skb: buffer to alter
   *	@mtu: maximum amount of headlen permitted
   *	@needed_tailroom: minimum amount of reserved_tailroom
   *
   *	Set reserved_tailroom so that headlen can be as large as possible but
   *	not larger than mtu and tailroom cannot be smaller than
   *	needed_tailroom.
   *	The required headroom should already have been reserved before using
   *	this function.
   */
  static inline void skb_tailroom_reserve(struct sk_buff *skb, unsigned int mtu,
  					unsigned int needed_tailroom)
  {
  	SKB_LINEAR_ASSERT(skb);
  	if (mtu < skb_tailroom(skb) - needed_tailroom)
  		/* use at most mtu */
  		skb->reserved_tailroom = skb_tailroom(skb) - mtu;
  	else
  		/* use up to all available space */
  		skb->reserved_tailroom = needed_tailroom;
  }
  
  #define ENCAP_TYPE_ETHER	0
  #define ENCAP_TYPE_IPPROTO	1
  
  static inline void skb_set_inner_protocol(struct sk_buff *skb,
  					  __be16 protocol)
  {
  	skb->inner_protocol = protocol;
  	skb->inner_protocol_type = ENCAP_TYPE_ETHER;
  }
  
  static inline void skb_set_inner_ipproto(struct sk_buff *skb,
  					 __u8 ipproto)
  {
  	skb->inner_ipproto = ipproto;
  	skb->inner_protocol_type = ENCAP_TYPE_IPPROTO;
  }
  
  static inline void skb_reset_inner_headers(struct sk_buff *skb)
  {
  	skb->inner_mac_header = skb->mac_header;
  	skb->inner_network_header = skb->network_header;
  	skb->inner_transport_header = skb->transport_header;
  }
  
  static inline void skb_reset_mac_len(struct sk_buff *skb)
  {
  	skb->mac_len = skb->network_header - skb->mac_header;
  }
  
  static inline unsigned char *skb_inner_transport_header(const struct sk_buff
  							*skb)
  {
  	return skb->head + skb->inner_transport_header;
  }
  
  static inline int skb_inner_transport_offset(const struct sk_buff *skb)
  {
  	return skb_inner_transport_header(skb) - skb->data;
  }
  
  static inline void skb_reset_inner_transport_header(struct sk_buff *skb)
  {
  	skb->inner_transport_header = skb->data - skb->head;
  }
  
  static inline void skb_set_inner_transport_header(struct sk_buff *skb,
  						   const int offset)
  {
  	skb_reset_inner_transport_header(skb);
  	skb->inner_transport_header += offset;
  }
  
  static inline unsigned char *skb_inner_network_header(const struct sk_buff *skb)
  {
  	return skb->head + skb->inner_network_header;
  }
  
  static inline void skb_reset_inner_network_header(struct sk_buff *skb)
  {
  	skb->inner_network_header = skb->data - skb->head;
  }
  
  static inline void skb_set_inner_network_header(struct sk_buff *skb,
  						const int offset)
  {
  	skb_reset_inner_network_header(skb);
  	skb->inner_network_header += offset;
  }
  
  static inline unsigned char *skb_inner_mac_header(const struct sk_buff *skb)
  {
  	return skb->head + skb->inner_mac_header;
  }
  
  static inline void skb_reset_inner_mac_header(struct sk_buff *skb)
  {
  	skb->inner_mac_header = skb->data - skb->head;
  }
  
  static inline void skb_set_inner_mac_header(struct sk_buff *skb,
  					    const int offset)
  {
  	skb_reset_inner_mac_header(skb);
  	skb->inner_mac_header += offset;
  }
  static inline bool skb_transport_header_was_set(const struct sk_buff *skb)
  {
  	return skb->transport_header != (typeof(skb->transport_header))~0U;
  }
  
  static inline unsigned char *skb_transport_header(const struct sk_buff *skb)
  {
  	return skb->head + skb->transport_header;
  }
  
  static inline void skb_reset_transport_header(struct sk_buff *skb)
  {
  	skb->transport_header = skb->data - skb->head;
  }
  
  static inline void skb_set_transport_header(struct sk_buff *skb,
  					    const int offset)
  {
  	skb_reset_transport_header(skb);
  	skb->transport_header += offset;
  }
  
  static inline unsigned char *skb_network_header(const struct sk_buff *skb)
  {
  	return skb->head + skb->network_header;
  }
  
  static inline void skb_reset_network_header(struct sk_buff *skb)
  {
  	skb->network_header = skb->data - skb->head;
  }
  
  static inline void skb_set_network_header(struct sk_buff *skb, const int offset)
  {
  	skb_reset_network_header(skb);
  	skb->network_header += offset;
  }
  
  static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
  {
  	return skb->head + skb->mac_header;
  }
  
  static inline int skb_mac_offset(const struct sk_buff *skb)
  {
  	return skb_mac_header(skb) - skb->data;
  }
  
  static inline u32 skb_mac_header_len(const struct sk_buff *skb)
  {
  	return skb->network_header - skb->mac_header;
  }
  
  static inline int skb_mac_header_was_set(const struct sk_buff *skb)
  {
  	return skb->mac_header != (typeof(skb->mac_header))~0U;
  }
  
  static inline void skb_unset_mac_header(struct sk_buff *skb)
  {
  	skb->mac_header = (typeof(skb->mac_header))~0U;
  }
  
  static inline void skb_reset_mac_header(struct sk_buff *skb)
  {
  	skb->mac_header = skb->data - skb->head;
  }
  
  static inline void skb_set_mac_header(struct sk_buff *skb, const int offset)
  {
  	skb_reset_mac_header(skb);
  	skb->mac_header += offset;
  }
  
  static inline void skb_pop_mac_header(struct sk_buff *skb)
  {
  	skb->mac_header = skb->network_header;
  }
  
  static inline void skb_probe_transport_header(struct sk_buff *skb)
  {
  	struct flow_keys_basic keys;
  
  	if (skb_transport_header_was_set(skb))
  		return;
  
  	if (skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
  					     NULL, 0, 0, 0, 0))
  		skb_set_transport_header(skb, keys.control.thoff);
  }
  
  static inline void skb_mac_header_rebuild(struct sk_buff *skb)
  {
  	if (skb_mac_header_was_set(skb)) {
  		const unsigned char *old_mac = skb_mac_header(skb);
  
  		skb_set_mac_header(skb, -skb->mac_len);
  		memmove(skb_mac_header(skb), old_mac, skb->mac_len);
  	}
  }
  
  static inline int skb_checksum_start_offset(const struct sk_buff *skb)
  {
  	return skb->csum_start - skb_headroom(skb);
  }
  
  static inline unsigned char *skb_checksum_start(const struct sk_buff *skb)
  {
  	return skb->head + skb->csum_start;
  }
  
  static inline int skb_transport_offset(const struct sk_buff *skb)
  {
  	return skb_transport_header(skb) - skb->data;
  }
  
  static inline u32 skb_network_header_len(const struct sk_buff *skb)
  {
  	return skb->transport_header - skb->network_header;
  }
  
  static inline u32 skb_inner_network_header_len(const struct sk_buff *skb)
  {
  	return skb->inner_transport_header - skb->inner_network_header;
  }
  
  static inline int skb_network_offset(const struct sk_buff *skb)
  {
  	return skb_network_header(skb) - skb->data;
  }
  
  static inline int skb_inner_network_offset(const struct sk_buff *skb)
  {
  	return skb_inner_network_header(skb) - skb->data;
  }
  
  static inline int pskb_network_may_pull(struct sk_buff *skb, unsigned int len)
  {
  	return pskb_may_pull(skb, skb_network_offset(skb) + len);
  }
  
  /*
   * CPUs often take a performance hit when accessing unaligned memory
   * locations. The actual performance hit varies, it can be small if the
   * hardware handles it or large if we have to take an exception and fix it
   * in software.
   *
   * Since an ethernet header is 14 bytes network drivers often end up with
   * the IP header at an unaligned offset. The IP header can be aligned by
   * shifting the start of the packet by 2 bytes. Drivers should do this
   * with:
   *
   * skb_reserve(skb, NET_IP_ALIGN);
   *
   * The downside to this alignment of the IP header is that the DMA is now
   * unaligned. On some architectures the cost of an unaligned DMA is high
   * and this cost outweighs the gains made by aligning the IP header.
   *
   * Since this trade off varies between architectures, we allow NET_IP_ALIGN
   * to be overridden.
   */
  #ifndef NET_IP_ALIGN
  #define NET_IP_ALIGN	2
  #endif
  
  /*
   * The networking layer reserves some headroom in skb data (via
   * dev_alloc_skb). This is used to avoid having to reallocate skb data when
   * the header has to grow. In the default case, if the header has to grow
   * 32 bytes or less we avoid the reallocation.
   *
   * Unfortunately this headroom changes the DMA alignment of the resulting
   * network packet. As for NET_IP_ALIGN, this unaligned DMA is expensive
   * on some architectures. An architecture can override this value,
   * perhaps setting it to a cacheline in size (since that will maintain
   * cacheline alignment of the DMA). It must be a power of 2.
   *
   * Various parts of the networking layer expect at least 32 bytes of
   * headroom, you should not reduce this.
   *
   * Using max(32, L1_CACHE_BYTES) makes sense (especially with RPS)
   * to reduce average number of cache lines per packet.
   * get_rps_cpu() for example only access one 64 bytes aligned block :
   * NET_IP_ALIGN(2) + ethernet_header(14) + IP_header(20/40) + ports(8)
   */
  #ifndef NET_SKB_PAD
  #define NET_SKB_PAD	max(32, L1_CACHE_BYTES)
  #endif
  
  int ___pskb_trim(struct sk_buff *skb, unsigned int len);
  
  static inline void __skb_set_length(struct sk_buff *skb, unsigned int len)
  {
  	if (WARN_ON(skb_is_nonlinear(skb)))
  		return;
  	skb->len = len;
  	skb_set_tail_pointer(skb, len);
  }
  
  static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
  {
  	__skb_set_length(skb, len);
  }
  
  void skb_trim(struct sk_buff *skb, unsigned int len);
  
  static inline int __pskb_trim(struct sk_buff *skb, unsigned int len)
  {
  	if (skb->data_len)
  		return ___pskb_trim(skb, len);
  	__skb_trim(skb, len);
  	return 0;
  }
  
  static inline int pskb_trim(struct sk_buff *skb, unsigned int len)
  {
  	return (len < skb->len) ? __pskb_trim(skb, len) : 0;
  }
  
  /**
   *	pskb_trim_unique - remove end from a paged unique (not cloned) buffer
   *	@skb: buffer to alter
   *	@len: new length
   *
   *	This is identical to pskb_trim except that the caller knows that
   *	the skb is not cloned so we should never get an error due to out-
   *	of-memory.
   */
  static inline void pskb_trim_unique(struct sk_buff *skb, unsigned int len)
  {
  	int err = pskb_trim(skb, len);
  	BUG_ON(err);
  }
  
  static inline int __skb_grow(struct sk_buff *skb, unsigned int len)
  {
  	unsigned int diff = len - skb->len;
  
  	if (skb_tailroom(skb) < diff) {
  		int ret = pskb_expand_head(skb, 0, diff - skb_tailroom(skb),
  					   GFP_ATOMIC);
  		if (ret)
  			return ret;
  	}
  	__skb_set_length(skb, len);
  	return 0;
  }
  
  /**
   *	skb_orphan - orphan a buffer
   *	@skb: buffer to orphan
   *
   *	If a buffer currently has an owner then we call the owner's
   *	destructor function and make the @skb unowned. The buffer continues
   *	to exist but is no longer charged to its former owner.
   */
  static inline void skb_orphan(struct sk_buff *skb)
  {
  	if (skb->destructor) {
  		skb->destructor(skb);
  		skb->destructor = NULL;
  		skb->sk		= NULL;
  	} else {
  		BUG_ON(skb->sk);
  	}
  }
  
  /**
   *	skb_orphan_frags - orphan the frags contained in a buffer
   *	@skb: buffer to orphan frags from
   *	@gfp_mask: allocation mask for replacement pages
   *
   *	For each frag in the SKB which needs a destructor (i.e. has an
   *	owner) create a copy of that frag and release the original
   *	page by calling the destructor.
   */
  static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
  {
  	if (likely(!skb_zcopy(skb)))
  		return 0;
  	if (!skb_zcopy_is_nouarg(skb) &&
  	    skb_uarg(skb)->callback == sock_zerocopy_callback)
  		return 0;
  	return skb_copy_ubufs(skb, gfp_mask);
  }
  
  /* Frags must be orphaned, even if refcounted, if skb might loop to rx path */
  static inline int skb_orphan_frags_rx(struct sk_buff *skb, gfp_t gfp_mask)
  {
  	if (likely(!skb_zcopy(skb)))
  		return 0;
  	return skb_copy_ubufs(skb, gfp_mask);
  }
  
  /**
   *	__skb_queue_purge - empty a list
   *	@list: list to empty
   *
   *	Delete all buffers on an &sk_buff list. Each buffer is removed from
   *	the list and one reference dropped. This function does not take the
   *	list lock and the caller must hold the relevant locks to use it.
   */
  static inline void __skb_queue_purge(struct sk_buff_head *list)
  {
  	struct sk_buff *skb;
  	while ((skb = __skb_dequeue(list)) != NULL)
  		kfree_skb(skb);
  }
  void skb_queue_purge(struct sk_buff_head *list);
  
  unsigned int skb_rbtree_purge(struct rb_root *root);
  
  void *netdev_alloc_frag(unsigned int fragsz);
  
  struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int length,
  				   gfp_t gfp_mask);
  
  /**
   *	netdev_alloc_skb - allocate an skbuff for rx on a specific device
   *	@dev: network device to receive on
   *	@length: length to allocate
   *
   *	Allocate a new &sk_buff and assign it a usage count of one. The
   *	buffer has unspecified headroom built in. Users should allocate
   *	the headroom they think they need without accounting for the
   *	built in space. The built in space is used for optimisations.
   *
   *	%NULL is returned if there is no free memory. Although this function
   *	allocates memory it can be called from an interrupt.
   */
  static inline struct sk_buff *netdev_alloc_skb(struct net_device *dev,
  					       unsigned int length)
  {
  	return __netdev_alloc_skb(dev, length, GFP_ATOMIC);
  }
  
  /* legacy helper around __netdev_alloc_skb() */
  static inline struct sk_buff *__dev_alloc_skb(unsigned int length,
  					      gfp_t gfp_mask)
  {
  	return __netdev_alloc_skb(NULL, length, gfp_mask);
  }
  
  /* legacy helper around netdev_alloc_skb() */
  static inline struct sk_buff *dev_alloc_skb(unsigned int length)
  {
  	return netdev_alloc_skb(NULL, length);
  }
  
  
  static inline struct sk_buff *__netdev_alloc_skb_ip_align(struct net_device *dev,
  		unsigned int length, gfp_t gfp)
  {
  	struct sk_buff *skb = __netdev_alloc_skb(dev, length + NET_IP_ALIGN, gfp);
  
  	if (NET_IP_ALIGN && skb)
  		skb_reserve(skb, NET_IP_ALIGN);
  	return skb;
  }
  
  static inline struct sk_buff *netdev_alloc_skb_ip_align(struct net_device *dev,
  		unsigned int length)
  {
  	return __netdev_alloc_skb_ip_align(dev, length, GFP_ATOMIC);
  }
  
  static inline void skb_free_frag(void *addr)
  {
  	page_frag_free(addr);
  }
  
  void *napi_alloc_frag(unsigned int fragsz);
  struct sk_buff *__napi_alloc_skb(struct napi_struct *napi,
  				 unsigned int length, gfp_t gfp_mask);
  static inline struct sk_buff *napi_alloc_skb(struct napi_struct *napi,
  					     unsigned int length)
  {
  	return __napi_alloc_skb(napi, length, GFP_ATOMIC);
  }
  void napi_consume_skb(struct sk_buff *skb, int budget);
  
  void __kfree_skb_flush(void);
  void __kfree_skb_defer(struct sk_buff *skb);
  
  /**
   * __dev_alloc_pages - allocate page for network Rx
   * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
   * @order: size of the allocation
   *
   * Allocate a new page.
   *
   * %NULL is returned if there is no free memory.
  */
  static inline struct page *__dev_alloc_pages(gfp_t gfp_mask,
  					     unsigned int order)
  {
  	/* This piece of code contains several assumptions.
  	 * 1.  This is for device Rx, therefor a cold page is preferred.
  	 * 2.  The expectation is the user wants a compound page.
  	 * 3.  If requesting a order 0 page it will not be compound
  	 *     due to the check to see if order has a value in prep_new_page
  	 * 4.  __GFP_MEMALLOC is ignored if __GFP_NOMEMALLOC is set due to
  	 *     code in gfp_to_alloc_flags that should be enforcing this.
  	 */
  	gfp_mask |= __GFP_COMP | __GFP_MEMALLOC;
  
  	return alloc_pages_node(NUMA_NO_NODE, gfp_mask, order);
  }
  
  static inline struct page *dev_alloc_pages(unsigned int order)
  {
  	return __dev_alloc_pages(GFP_ATOMIC | __GFP_NOWARN, order);
  }
  
  /**
   * __dev_alloc_page - allocate a page for network Rx
   * @gfp_mask: allocation priority. Set __GFP_NOMEMALLOC if not for network Rx
   *
   * Allocate a new page.
   *
   * %NULL is returned if there is no free memory.
   */
  static inline struct page *__dev_alloc_page(gfp_t gfp_mask)
  {
  	return __dev_alloc_pages(gfp_mask, 0);
  }
  
  static inline struct page *dev_alloc_page(void)
  {
  	return dev_alloc_pages(0);
  }
  
  /**
   *	skb_propagate_pfmemalloc - Propagate pfmemalloc if skb is allocated after RX page
   *	@page: The page that was allocated from skb_alloc_page
   *	@skb: The skb that may need pfmemalloc set
   */
  static inline void skb_propagate_pfmemalloc(struct page *page,
  					     struct sk_buff *skb)
  {
  	if (page_is_pfmemalloc(page))
  		skb->pfmemalloc = true;
  }
  
  /**
   * skb_frag_off() - Returns the offset of a skb fragment
   * @frag: the paged fragment
   */
  static inline unsigned int skb_frag_off(const skb_frag_t *frag)
  {
  	return frag->bv_offset;
  }
  
  /**
   * skb_frag_off_add() - Increments the offset of a skb fragment by @delta
   * @frag: skb fragment
   * @delta: value to add
   */
  static inline void skb_frag_off_add(skb_frag_t *frag, int delta)
  {
  	frag->bv_offset += delta;
  }
  
  /**
   * skb_frag_off_set() - Sets the offset of a skb fragment
   * @frag: skb fragment
   * @offset: offset of fragment
   */
  static inline void skb_frag_off_set(skb_frag_t *frag, unsigned int offset)
  {
  	frag->bv_offset = offset;
  }
  
  /**
   * skb_frag_off_copy() - Sets the offset of a skb fragment from another fragment
   * @fragto: skb fragment where offset is set
   * @fragfrom: skb fragment offset is copied from
   */
  static inline void skb_frag_off_copy(skb_frag_t *fragto,
  				     const skb_frag_t *fragfrom)
  {
  	fragto->bv_offset = fragfrom->bv_offset;
  }
  
  /**
   * skb_frag_page - retrieve the page referred to by a paged fragment
   * @frag: the paged fragment
   *
   * Returns the &struct page associated with @frag.
   */
  static inline struct page *skb_frag_page(const skb_frag_t *frag)
  {
  	return frag->bv_page;
  }
  
  /**
   * __skb_frag_ref - take an addition reference on a paged fragment.
   * @frag: the paged fragment
   *
   * Takes an additional reference on the paged fragment @frag.
   */
  static inline void __skb_frag_ref(skb_frag_t *frag)
  {
  	get_page(skb_frag_page(frag));
  }
  
  /**
   * skb_frag_ref - take an addition reference on a paged fragment of an skb.
   * @skb: the buffer
   * @f: the fragment offset.
   *
   * Takes an additional reference on the @f'th paged fragment of @skb.
   */
  static inline void skb_frag_ref(struct sk_buff *skb, int f)
  {
  	__skb_frag_ref(&skb_shinfo(skb)->frags[f]);
  }
  
  /**
   * __skb_frag_unref - release a reference on a paged fragment.
   * @frag: the paged fragment
   *
   * Releases a reference on the paged fragment @frag.
   */
  static inline void __skb_frag_unref(skb_frag_t *frag)
  {
  	put_page(skb_frag_page(frag));
  }
  
  /**
   * skb_frag_unref - release a reference on a paged fragment of an skb.
   * @skb: the buffer
   * @f: the fragment offset
   *
   * Releases a reference on the @f'th paged fragment of @skb.
   */
  static inline void skb_frag_unref(struct sk_buff *skb, int f)
  {
  	__skb_frag_unref(&skb_shinfo(skb)->frags[f]);
  }
  
  /**
   * skb_frag_address - gets the address of the data contained in a paged fragment
   * @frag: the paged fragment buffer
   *
   * Returns the address of the data within @frag. The page must already
   * be mapped.
   */
  static inline void *skb_frag_address(const skb_frag_t *frag)
  {
  	return page_address(skb_frag_page(frag)) + skb_frag_off(frag);
  }
  
  /**
   * skb_frag_address_safe - gets the address of the data contained in a paged fragment
   * @frag: the paged fragment buffer
   *
   * Returns the address of the data within @frag. Checks that the page
   * is mapped and returns %NULL otherwise.
   */
  static inline void *skb_frag_address_safe(const skb_frag_t *frag)
  {
  	void *ptr = page_address(skb_frag_page(frag));
  	if (unlikely(!ptr))
  		return NULL;
  
  	return ptr + skb_frag_off(frag);
  }
  
  /**
   * skb_frag_page_copy() - sets the page in a fragment from another fragment
   * @fragto: skb fragment where page is set
   * @fragfrom: skb fragment page is copied from
   */
  static inline void skb_frag_page_copy(skb_frag_t *fragto,
  				      const skb_frag_t *fragfrom)
  {
  	fragto->bv_page = fragfrom->bv_page;
  }
  
  /**
   * __skb_frag_set_page - sets the page contained in a paged fragment
   * @frag: the paged fragment
   * @page: the page to set
   *
   * Sets the fragment @frag to contain @page.
   */
  static inline void __skb_frag_set_page(skb_frag_t *frag, struct page *page)
  {
  	frag->bv_page = page;
  }
  
  /**
   * skb_frag_set_page - sets the page contained in a paged fragment of an skb
   * @skb: the buffer
   * @f: the fragment offset
   * @page: the page to set
   *
   * Sets the @f'th fragment of @skb to contain @page.
   */
  static inline void skb_frag_set_page(struct sk_buff *skb, int f,
  				     struct page *page)
  {
  	__skb_frag_set_page(&skb_shinfo(skb)->frags[f], page);
  }
  
  bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t prio);
  
  /**
   * skb_frag_dma_map - maps a paged fragment via the DMA API
   * @dev: the device to map the fragment to
   * @frag: the paged fragment to map
   * @offset: the offset within the fragment (starting at the
   *          fragment's own offset)
   * @size: the number of bytes to map
   * @dir: the direction of the mapping (``PCI_DMA_*``)
   *
   * Maps the page associated with @frag to @device.
   */
  static inline dma_addr_t skb_frag_dma_map(struct device *dev,
  					  const skb_frag_t *frag,
  					  size_t offset, size_t size,
  					  enum dma_data_direction dir)
  {
  	return dma_map_page(dev, skb_frag_page(frag),
  			    skb_frag_off(frag) + offset, size, dir);
  }
  
  static inline struct sk_buff *pskb_copy(struct sk_buff *skb,
  					gfp_t gfp_mask)
  {
  	return __pskb_copy(skb, skb_headroom(skb), gfp_mask);
  }
  
  
  static inline struct sk_buff *pskb_copy_for_clone(struct sk_buff *skb,
  						  gfp_t gfp_mask)
  {
  	return __pskb_copy_fclone(skb, skb_headroom(skb), gfp_mask, true);
  }
  
  
  /**
   *	skb_clone_writable - is the header of a clone writable
   *	@skb: buffer to check
   *	@len: length up to which to write
   *
   *	Returns true if modifying the header part of the cloned buffer
   *	does not requires the data to be copied.
   */
  static inline int skb_clone_writable(const struct sk_buff *skb, unsigned int len)
  {
  	return !skb_header_cloned(skb) &&
  	       skb_headroom(skb) + len <= skb->hdr_len;
  }
  
  static inline int skb_try_make_writable(struct sk_buff *skb,
  					unsigned int write_len)
  {
  	return skb_cloned(skb) && !skb_clone_writable(skb, write_len) &&
  	       pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
  }
  
  static inline int __skb_cow(struct sk_buff *skb, unsigned int headroom,
  			    int cloned)
  {
  	int delta = 0;
  
  	if (headroom > skb_headroom(skb))
  		delta = headroom - skb_headroom(skb);
  
  	if (delta || cloned)
  		return pskb_expand_head(skb, ALIGN(delta, NET_SKB_PAD), 0,
  					GFP_ATOMIC);
  	return 0;
  }
  
  /**
   *	skb_cow - copy header of skb when it is required
   *	@skb: buffer to cow
   *	@headroom: needed headroom
   *
   *	If the skb passed lacks sufficient headroom or its data part
   *	is shared, data is reallocated. If reallocation fails, an error
   *	is returned and original skb is not changed.
   *
   *	The result is skb with writable area skb->head...skb->tail
   *	and at least @headroom of space at head.
   */
  static inline int skb_cow(struct sk_buff *skb, unsigned int headroom)
  {
  	return __skb_cow(skb, headroom, skb_cloned(skb));
  }
  
  /**
   *	skb_cow_head - skb_cow but only making the head writable
   *	@skb: buffer to cow
   *	@headroom: needed headroom
   *
   *	This function is identical to skb_cow except that we replace the
   *	skb_cloned check by skb_header_cloned.  It should be used when
   *	you only need to push on some header and do not need to modify
   *	the data.
   */
  static inline int skb_cow_head(struct sk_buff *skb, unsigned int headroom)
  {
  	return __skb_cow(skb, headroom, skb_header_cloned(skb));
  }
  
  /**
   *	skb_padto	- pad an skbuff up to a minimal size
   *	@skb: buffer to pad
   *	@len: minimal length
   *
   *	Pads up a buffer to ensure the trailing bytes exist and are
   *	blanked. If the buffer already contains sufficient data it
   *	is untouched. Otherwise it is extended. Returns zero on
   *	success. The skb is freed on error.
   */
  static inline int skb_padto(struct sk_buff *skb, unsigned int len)
  {
  	unsigned int size = skb->len;
  	if (likely(size >= len))
  		return 0;
  	return skb_pad(skb, len - size);
  }
  
  /**
   *	__skb_put_padto - increase size and pad an skbuff up to a minimal size
   *	@skb: buffer to pad
   *	@len: minimal length
   *	@free_on_error: free buffer on error
   *
   *	Pads up a buffer to ensure the trailing bytes exist and are
   *	blanked. If the buffer already contains sufficient data it
   *	is untouched. Otherwise it is extended. Returns zero on
   *	success. The skb is freed on error if @free_on_error is true.
   */
  static inline int __must_check __skb_put_padto(struct sk_buff *skb,
  					       unsigned int len,
  					       bool free_on_error)
  {
  	unsigned int size = skb->len;
  
  	if (unlikely(size < len)) {
  		len -= size;
  		if (__skb_pad(skb, len, free_on_error))
  			return -ENOMEM;
  		__skb_put(skb, len);
  	}
  	return 0;
  }
  
  /**
   *	skb_put_padto - increase size and pad an skbuff up to a minimal size
   *	@skb: buffer to pad
   *	@len: minimal length
   *
   *	Pads up a buffer to ensure the trailing bytes exist and are
   *	blanked. If the buffer already contains sufficient data it
   *	is untouched. Otherwise it is extended. Returns zero on
   *	success. The skb is freed on error.
   */
  static inline int __must_check skb_put_padto(struct sk_buff *skb, unsigned int len)
  {
  	return __skb_put_padto(skb, len, true);
  }
  
  static inline int skb_add_data(struct sk_buff *skb,
  			       struct iov_iter *from, int copy)
  {
  	const int off = skb->len;
  
  	if (skb->ip_summed == CHECKSUM_NONE) {
  		__wsum csum = 0;
  		if (csum_and_copy_from_iter_full(skb_put(skb, copy), copy,
  					         &csum, from)) {
  			skb->csum = csum_block_add(skb->csum, csum, off);
  			return 0;
  		}
  	} else if (copy_from_iter_full(skb_put(skb, copy), copy, from))
  		return 0;
  
  	__skb_trim(skb, off);
  	return -EFAULT;
  }
  
  static inline bool skb_can_coalesce(struct sk_buff *skb, int i,
  				    const struct page *page, int off)
  {
  	if (skb_zcopy(skb))
  		return false;
  	if (i) {
  		const skb_frag_t *frag = &skb_shinfo(skb)->frags[i - 1];
  
  		return page == skb_frag_page(frag) &&
  		       off == skb_frag_off(frag) + skb_frag_size(frag);
  	}
  	return false;
  }
  
  static inline int __skb_linearize(struct sk_buff *skb)
  {
  	return __pskb_pull_tail(skb, skb->data_len) ? 0 : -ENOMEM;
  }
  
  /**
   *	skb_linearize - convert paged skb to linear one
   *	@skb: buffer to linarize
   *
   *	If there is no free memory -ENOMEM is returned, otherwise zero
   *	is returned and the old skb data released.
   */
  static inline int skb_linearize(struct sk_buff *skb)
  {
  	return skb_is_nonlinear(skb) ? __skb_linearize(skb) : 0;
  }
  
  /**
   * skb_has_shared_frag - can any frag be overwritten
   * @skb: buffer to test
   *
   * Return true if the skb has at least one frag that might be modified
   * by an external entity (as in vmsplice()/sendfile())
   */
  static inline bool skb_has_shared_frag(const struct sk_buff *skb)
  {
  	return skb_is_nonlinear(skb) &&
  	       skb_shinfo(skb)->tx_flags & SKBTX_SHARED_FRAG;
  }
  
  /**
   *	skb_linearize_cow - make sure skb is linear and writable
   *	@skb: buffer to process
   *
   *	If there is no free memory -ENOMEM is returned, otherwise zero
   *	is returned and the old skb data released.
   */
  static inline int skb_linearize_cow(struct sk_buff *skb)
  {
  	return skb_is_nonlinear(skb) || skb_cloned(skb) ?
  	       __skb_linearize(skb) : 0;
  }
  
  static __always_inline void
  __skb_postpull_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
  		     unsigned int off)
  {
  	if (skb->ip_summed == CHECKSUM_COMPLETE)
  		skb->csum = csum_block_sub(skb->csum,
  					   csum_partial(start, len, 0), off);
  	else if (skb->ip_summed == CHECKSUM_PARTIAL &&
  		 skb_checksum_start_offset(skb) < 0)
  		skb->ip_summed = CHECKSUM_NONE;
  }
  
  /**
   *	skb_postpull_rcsum - update checksum for received skb after pull
   *	@skb: buffer to update
   *	@start: start of data before pull
   *	@len: length of data pulled
   *
   *	After doing a pull on a received packet, you need to call this to
   *	update the CHECKSUM_COMPLETE checksum, or set ip_summed to
   *	CHECKSUM_NONE so that it can be recomputed from scratch.
   */
  static inline void skb_postpull_rcsum(struct sk_buff *skb,
  				      const void *start, unsigned int len)
  {
  	__skb_postpull_rcsum(skb, start, len, 0);
  }
  
  static __always_inline void
  __skb_postpush_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
  		     unsigned int off)
  {
  	if (skb->ip_summed == CHECKSUM_COMPLETE)
  		skb->csum = csum_block_add(skb->csum,
  					   csum_partial(start, len, 0), off);
  }
  
  /**
   *	skb_postpush_rcsum - update checksum for received skb after push
   *	@skb: buffer to update
   *	@start: start of data after push
   *	@len: length of data pushed
   *
   *	After doing a push on a received packet, you need to call this to
   *	update the CHECKSUM_COMPLETE checksum.
   */
  static inline void skb_postpush_rcsum(struct sk_buff *skb,
  				      const void *start, unsigned int len)
  {
  	__skb_postpush_rcsum(skb, start, len, 0);
  }
  
  void *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
  
  /**
   *	skb_push_rcsum - push skb and update receive checksum
   *	@skb: buffer to update
   *	@len: length of data pulled
   *
   *	This function performs an skb_push on the packet and updates
   *	the CHECKSUM_COMPLETE checksum.  It should be used on
   *	receive path processing instead of skb_push unless you know
   *	that the checksum difference is zero (e.g., a valid IP header)
   *	or you are setting ip_summed to CHECKSUM_NONE.
   */
  static inline void *skb_push_rcsum(struct sk_buff *skb, unsigned int len)
  {
  	skb_push(skb, len);
  	skb_postpush_rcsum(skb, skb->data, len);
  	return skb->data;
  }
  
  int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len);
  /**
   *	pskb_trim_rcsum - trim received skb and update checksum
   *	@skb: buffer to trim
   *	@len: new length
   *
   *	This is exactly the same as pskb_trim except that it ensures the
   *	checksum of received packets are still valid after the operation.
   *	It can change skb pointers.
   */
  
  static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
  {
  	if (likely(len >= skb->len))
  		return 0;
  	return pskb_trim_rcsum_slow(skb, len);
  }
  
  static inline int __skb_trim_rcsum(struct sk_buff *skb, unsigned int len)
  {
  	if (skb->ip_summed == CHECKSUM_COMPLETE)
  		skb->ip_summed = CHECKSUM_NONE;
  	__skb_trim(skb, len);
  	return 0;
  }
  
  static inline int __skb_grow_rcsum(struct sk_buff *skb, unsigned int len)
  {
  	if (skb->ip_summed == CHECKSUM_COMPLETE)
  		skb->ip_summed = CHECKSUM_NONE;
  	return __skb_grow(skb, len);
  }
  
  #define rb_to_skb(rb) rb_entry_safe(rb, struct sk_buff, rbnode)
  #define skb_rb_first(root) rb_to_skb(rb_first(root))
  #define skb_rb_last(root)  rb_to_skb(rb_last(root))
  #define skb_rb_next(skb)   rb_to_skb(rb_next(&(skb)->rbnode))
  #define skb_rb_prev(skb)   rb_to_skb(rb_prev(&(skb)->rbnode))
  
  #define skb_queue_walk(queue, skb) \
  		for (skb = (queue)->next;					\
  		     skb != (struct sk_buff *)(queue);				\
  		     skb = skb->next)
  
  #define skb_queue_walk_safe(queue, skb, tmp)					\
  		for (skb = (queue)->next, tmp = skb->next;			\
  		     skb != (struct sk_buff *)(queue);				\
  		     skb = tmp, tmp = skb->next)
  
  #define skb_queue_walk_from(queue, skb)						\
  		for (; skb != (struct sk_buff *)(queue);			\
  		     skb = skb->next)
  
  #define skb_rbtree_walk(skb, root)						\
  		for (skb = skb_rb_first(root); skb != NULL;			\
  		     skb = skb_rb_next(skb))
  
  #define skb_rbtree_walk_from(skb)						\
  		for (; skb != NULL;						\
  		     skb = skb_rb_next(skb))
  
  #define skb_rbtree_walk_from_safe(skb, tmp)					\
  		for (; tmp = skb ? skb_rb_next(skb) : NULL, (skb != NULL);	\
  		     skb = tmp)
  
  #define skb_queue_walk_from_safe(queue, skb, tmp)				\
  		for (tmp = skb->next;						\
  		     skb != (struct sk_buff *)(queue);				\
  		     skb = tmp, tmp = skb->next)
  
  #define skb_queue_reverse_walk(queue, skb) \
  		for (skb = (queue)->prev;					\
  		     skb != (struct sk_buff *)(queue);				\
  		     skb = skb->prev)
  
  #define skb_queue_reverse_walk_safe(queue, skb, tmp)				\
  		for (skb = (queue)->prev, tmp = skb->prev;			\
  		     skb != (struct sk_buff *)(queue);				\
  		     skb = tmp, tmp = skb->prev)
  
  #define skb_queue_reverse_walk_from_safe(queue, skb, tmp)			\
  		for (tmp = skb->prev;						\
  		     skb != (struct sk_buff *)(queue);				\
  		     skb = tmp, tmp = skb->prev)
  
  static inline bool skb_has_frag_list(const struct sk_buff *skb)
  {
  	return skb_shinfo(skb)->frag_list != NULL;
  }
  
  static inline void skb_frag_list_init(struct sk_buff *skb)
  {
  	skb_shinfo(skb)->frag_list = NULL;
  }
  
  #define skb_walk_frags(skb, iter)	\
  	for (iter = skb_shinfo(skb)->frag_list; iter; iter = iter->next)
  
  
  int __skb_wait_for_more_packets(struct sock *sk, struct sk_buff_head *queue,
  				int *err, long *timeo_p,
  				const struct sk_buff *skb);
  struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
  					  struct sk_buff_head *queue,
  					  unsigned int flags,
  					  int *off, int *err,
  					  struct sk_buff **last);
  struct sk_buff *__skb_try_recv_datagram(struct sock *sk,
  					struct sk_buff_head *queue,
  					unsigned int flags, int *off, int *err,
  					struct sk_buff **last);
  struct sk_buff *__skb_recv_datagram(struct sock *sk,
  				    struct sk_buff_head *sk_queue,
  				    unsigned int flags, int *off, int *err);
  struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned flags, int noblock,
  				  int *err);
  __poll_t datagram_poll(struct file *file, struct socket *sock,
  			   struct poll_table_struct *wait);
  int skb_copy_datagram_iter(const struct sk_buff *from, int offset,
  			   struct iov_iter *to, int size);
  static inline int skb_copy_datagram_msg(const struct sk_buff *from, int offset,
  					struct msghdr *msg, int size)
  {
  	return skb_copy_datagram_iter(from, offset, &msg->msg_iter, size);
  }
  int skb_copy_and_csum_datagram_msg(struct sk_buff *skb, int hlen,
  				   struct msghdr *msg);
  int skb_copy_and_hash_datagram_iter(const struct sk_buff *skb, int offset,
  			   struct iov_iter *to, int len,
  			   struct ahash_request *hash);
  int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
  				 struct iov_iter *from, int len);
  int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *frm);
  void skb_free_datagram(struct sock *sk, struct sk_buff *skb);
  void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len);
  static inline void skb_free_datagram_locked(struct sock *sk,
  					    struct sk_buff *skb)
  {
  	__skb_free_datagram_locked(sk, skb, 0);
  }
  int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags);
  int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len);
  int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len);
  __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset, u8 *to,
  			      int len);
  int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
  		    struct pipe_inode_info *pipe, unsigned int len,
  		    unsigned int flags);
  int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
  			 int len);
  void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
  unsigned int skb_zerocopy_headlen(const struct sk_buff *from);
  int skb_zerocopy(struct sk_buff *to, struct sk_buff *from,
  		 int len, int hlen);
  void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len);
  int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen);
  void skb_scrub_packet(struct sk_buff *skb, bool xnet);
  bool skb_gso_validate_network_len(const struct sk_buff *skb, unsigned int mtu);
  bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len);
  struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
  struct sk_buff *skb_segment_list(struct sk_buff *skb, netdev_features_t features,
  				 unsigned int offset);
  struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
  int skb_ensure_writable(struct sk_buff *skb, int write_len);
  int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci);
  int skb_vlan_pop(struct sk_buff *skb);
  int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci);
  int skb_eth_pop(struct sk_buff *skb);
  int skb_eth_push(struct sk_buff *skb, const unsigned char *dst,
  		 const unsigned char *src);
  int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto,
  		  int mac_len, bool ethernet);
  int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len,
  		 bool ethernet);
  int skb_mpls_update_lse(struct sk_buff *skb, __be32 mpls_lse);
  int skb_mpls_dec_ttl(struct sk_buff *skb);
  struct sk_buff *pskb_extract(struct sk_buff *skb, int off, int to_copy,
  			     gfp_t gfp);
  
  static inline int memcpy_from_msg(void *data, struct msghdr *msg, int len)
  {
  	return copy_from_iter_full(data, len, &msg->msg_iter) ? 0 : -EFAULT;
  }
  
  static inline int memcpy_to_msg(struct msghdr *msg, void *data, int len)
  {
  	return copy_to_iter(data, len, &msg->msg_iter) == len ? 0 : -EFAULT;
  }
  
  struct skb_checksum_ops {
  	__wsum (*update)(const void *mem, int len, __wsum wsum);
  	__wsum (*combine)(__wsum csum, __wsum csum2, int offset, int len);
  };
  
  extern const struct skb_checksum_ops *crc32c_csum_stub __read_mostly;
  
  __wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
  		      __wsum csum, const struct skb_checksum_ops *ops);
  __wsum skb_checksum(const struct sk_buff *skb, int offset, int len,
  		    __wsum csum);
  
  static inline void * __must_check
  __skb_header_pointer(const struct sk_buff *skb, int offset,
  		     int len, void *data, int hlen, void *buffer)
  {
  	if (hlen - offset >= len)
  		return data + offset;
  
  	if (!skb ||
  	    skb_copy_bits(skb, offset, buffer, len) < 0)
  		return NULL;
  
  	return buffer;
  }
  
  static inline void * __must_check
  skb_header_pointer(const struct sk_buff *skb, int offset, int len, void *buffer)
  {
  	return __skb_header_pointer(skb, offset, len, skb->data,
  				    skb_headlen(skb), buffer);
  }
  
  /**
   *	skb_needs_linearize - check if we need to linearize a given skb
   *			      depending on the given device features.
   *	@skb: socket buffer to check
   *	@features: net device features
   *
   *	Returns true if either:
   *	1. skb has frag_list and the device doesn't support FRAGLIST, or
   *	2. skb is fragmented and the device does not support SG.
   */
  static inline bool skb_needs_linearize(struct sk_buff *skb,
  				       netdev_features_t features)
  {
  	return skb_is_nonlinear(skb) &&
  	       ((skb_has_frag_list(skb) && !(features & NETIF_F_FRAGLIST)) ||
  		(skb_shinfo(skb)->nr_frags && !(features & NETIF_F_SG)));
  }
  
  static inline void skb_copy_from_linear_data(const struct sk_buff *skb,
  					     void *to,
  					     const unsigned int len)
  {
  	memcpy(to, skb->data, len);
  }
  
  static inline void skb_copy_from_linear_data_offset(const struct sk_buff *skb,
  						    const int offset, void *to,
  						    const unsigned int len)
  {
  	memcpy(to, skb->data + offset, len);
  }
  
  static inline void skb_copy_to_linear_data(struct sk_buff *skb,
  					   const void *from,
  					   const unsigned int len)
  {
  	memcpy(skb->data, from, len);
  }
  
  static inline void skb_copy_to_linear_data_offset(struct sk_buff *skb,
  						  const int offset,
  						  const void *from,
  						  const unsigned int len)
  {
  	memcpy(skb->data + offset, from, len);
  }
  
  void skb_init(void);
  
  static inline ktime_t skb_get_ktime(const struct sk_buff *skb)
  {
  	return skb->tstamp;
  }
  
  /**
   *	skb_get_timestamp - get timestamp from a skb
   *	@skb: skb to get stamp from
   *	@stamp: pointer to struct __kernel_old_timeval to store stamp in
   *
   *	Timestamps are stored in the skb as offsets to a base timestamp.
   *	This function converts the offset back to a struct timeval and stores
   *	it in stamp.
   */
  static inline void skb_get_timestamp(const struct sk_buff *skb,
  				     struct __kernel_old_timeval *stamp)
  {
  	*stamp = ns_to_kernel_old_timeval(skb->tstamp);
  }
  
  static inline void skb_get_new_timestamp(const struct sk_buff *skb,
  					 struct __kernel_sock_timeval *stamp)
  {
  	struct timespec64 ts = ktime_to_timespec64(skb->tstamp);
  
  	stamp->tv_sec = ts.tv_sec;
  	stamp->tv_usec = ts.tv_nsec / 1000;
  }
  
  static inline void skb_get_timestampns(const struct sk_buff *skb,
  				       struct __kernel_old_timespec *stamp)
  {
  	struct timespec64 ts = ktime_to_timespec64(skb->tstamp);
  
  	stamp->tv_sec = ts.tv_sec;
  	stamp->tv_nsec = ts.tv_nsec;
  }
  
  static inline void skb_get_new_timestampns(const struct sk_buff *skb,
  					   struct __kernel_timespec *stamp)
  {
  	struct timespec64 ts = ktime_to_timespec64(skb->tstamp);
  
  	stamp->tv_sec = ts.tv_sec;
  	stamp->tv_nsec = ts.tv_nsec;
  }
  
  static inline void __net_timestamp(struct sk_buff *skb)
  {
  	skb->tstamp = ktime_get_real();
  }
  
  static inline ktime_t net_timedelta(ktime_t t)
  {
  	return ktime_sub(ktime_get_real(), t);
  }
  
  static inline ktime_t net_invalid_timestamp(void)
  {
  	return 0;
  }
  
  static inline u8 skb_metadata_len(const struct sk_buff *skb)
  {
  	return skb_shinfo(skb)->meta_len;
  }
  
  static inline void *skb_metadata_end(const struct sk_buff *skb)
  {
  	return skb_mac_header(skb);
  }
  
  static inline bool __skb_metadata_differs(const struct sk_buff *skb_a,
  					  const struct sk_buff *skb_b,
  					  u8 meta_len)
  {
  	const void *a = skb_metadata_end(skb_a);
  	const void *b = skb_metadata_end(skb_b);
  	/* Using more efficient varaiant than plain call to memcmp(). */
  #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
  	u64 diffs = 0;
  
  	switch (meta_len) {
  #define __it(x, op) (x -= sizeof(u##op))
  #define __it_diff(a, b, op) (*(u##op *)__it(a, op)) ^ (*(u##op *)__it(b, op))
  	case 32: diffs |= __it_diff(a, b, 64);
  		fallthrough;
  	case 24: diffs |= __it_diff(a, b, 64);
  		fallthrough;
  	case 16: diffs |= __it_diff(a, b, 64);
  		fallthrough;
  	case  8: diffs |= __it_diff(a, b, 64);
  		break;
  	case 28: diffs |= __it_diff(a, b, 64);
  		fallthrough;
  	case 20: diffs |= __it_diff(a, b, 64);
  		fallthrough;
  	case 12: diffs |= __it_diff(a, b, 64);
  		fallthrough;
  	case  4: diffs |= __it_diff(a, b, 32);
  		break;
  	}
  	return diffs;
  #else
  	return memcmp(a - meta_len, b - meta_len, meta_len);
  #endif
  }
  
  static inline bool skb_metadata_differs(const struct sk_buff *skb_a,
  					const struct sk_buff *skb_b)
  {
  	u8 len_a = skb_metadata_len(skb_a);
  	u8 len_b = skb_metadata_len(skb_b);
  
  	if (!(len_a | len_b))
  		return false;
  
  	return len_a != len_b ?
  	       true : __skb_metadata_differs(skb_a, skb_b, len_a);
  }
  
  static inline void skb_metadata_set(struct sk_buff *skb, u8 meta_len)
  {
  	skb_shinfo(skb)->meta_len = meta_len;
  }
  
  static inline void skb_metadata_clear(struct sk_buff *skb)
  {
  	skb_metadata_set(skb, 0);
  }
  
  struct sk_buff *skb_clone_sk(struct sk_buff *skb);
  
  #ifdef CONFIG_NETWORK_PHY_TIMESTAMPING
  
  void skb_clone_tx_timestamp(struct sk_buff *skb);
  bool skb_defer_rx_timestamp(struct sk_buff *skb);
  
  #else /* CONFIG_NETWORK_PHY_TIMESTAMPING */
  
  static inline void skb_clone_tx_timestamp(struct sk_buff *skb)
  {
  }
  
  static inline bool skb_defer_rx_timestamp(struct sk_buff *skb)
  {
  	return false;
  }
  
  #endif /* !CONFIG_NETWORK_PHY_TIMESTAMPING */
  
  /**
   * skb_complete_tx_timestamp() - deliver cloned skb with tx timestamps
   *
   * PHY drivers may accept clones of transmitted packets for
   * timestamping via their phy_driver.txtstamp method. These drivers
   * must call this function to return the skb back to the stack with a
   * timestamp.
   *
   * @skb: clone of the original outgoing packet
   * @hwtstamps: hardware time stamps
   *
   */
  void skb_complete_tx_timestamp(struct sk_buff *skb,
  			       struct skb_shared_hwtstamps *hwtstamps);
  
  void __skb_tstamp_tx(struct sk_buff *orig_skb,
  		     struct skb_shared_hwtstamps *hwtstamps,
  		     struct sock *sk, int tstype);
  
  /**
   * skb_tstamp_tx - queue clone of skb with send time stamps
   * @orig_skb:	the original outgoing packet
   * @hwtstamps:	hardware time stamps, may be NULL if not available
   *
   * If the skb has a socket associated, then this function clones the
   * skb (thus sharing the actual data and optional structures), stores
   * the optional hardware time stamping information (if non NULL) or
   * generates a software time stamp (otherwise), then queues the clone
   * to the error queue of the socket.  Errors are silently ignored.
   */
  void skb_tstamp_tx(struct sk_buff *orig_skb,
  		   struct skb_shared_hwtstamps *hwtstamps);
  
  /**
   * skb_tx_timestamp() - Driver hook for transmit timestamping
   *
   * Ethernet MAC Drivers should call this function in their hard_xmit()
   * function immediately before giving the sk_buff to the MAC hardware.
   *
   * Specifically, one should make absolutely sure that this function is
   * called before TX completion of this packet can trigger.  Otherwise
   * the packet could potentially already be freed.
   *
   * @skb: A socket buffer.
   */
  static inline void skb_tx_timestamp(struct sk_buff *skb)
  {
  	skb_clone_tx_timestamp(skb);
  	if (skb_shinfo(skb)->tx_flags & SKBTX_SW_TSTAMP)
  		skb_tstamp_tx(skb, NULL);
  }
  
  /**
   * skb_complete_wifi_ack - deliver skb with wifi status
   *
   * @skb: the original outgoing packet
   * @acked: ack status
   *
   */
  void skb_complete_wifi_ack(struct sk_buff *skb, bool acked);
  
  __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len);
  __sum16 __skb_checksum_complete(struct sk_buff *skb);
  
  static inline int skb_csum_unnecessary(const struct sk_buff *skb)
  {
  	return ((skb->ip_summed == CHECKSUM_UNNECESSARY) ||
  		skb->csum_valid ||
  		(skb->ip_summed == CHECKSUM_PARTIAL &&
  		 skb_checksum_start_offset(skb) >= 0));
  }
  
  /**
   *	skb_checksum_complete - Calculate checksum of an entire packet
   *	@skb: packet to process
   *
   *	This function calculates the checksum over the entire packet plus
   *	the value of skb->csum.  The latter can be used to supply the
   *	checksum of a pseudo header as used by TCP/UDP.  It returns the
   *	checksum.
   *
   *	For protocols that contain complete checksums such as ICMP/TCP/UDP,
   *	this function can be used to verify that checksum on received
   *	packets.  In that case the function should return zero if the
   *	checksum is correct.  In particular, this function will return zero
   *	if skb->ip_summed is CHECKSUM_UNNECESSARY which indicates that the
   *	hardware has already verified the correctness of the checksum.
   */
  static inline __sum16 skb_checksum_complete(struct sk_buff *skb)
  {
  	return skb_csum_unnecessary(skb) ?
  	       0 : __skb_checksum_complete(skb);
  }
  
  static inline void __skb_decr_checksum_unnecessary(struct sk_buff *skb)
  {
  	if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
  		if (skb->csum_level == 0)
  			skb->ip_summed = CHECKSUM_NONE;
  		else
  			skb->csum_level--;
  	}
  }
  
  static inline void __skb_incr_checksum_unnecessary(struct sk_buff *skb)
  {
  	if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
  		if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
  			skb->csum_level++;
  	} else if (skb->ip_summed == CHECKSUM_NONE) {
  		skb->ip_summed = CHECKSUM_UNNECESSARY;
  		skb->csum_level = 0;
  	}
  }
  
  static inline void __skb_reset_checksum_unnecessary(struct sk_buff *skb)
  {
  	if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
  		skb->ip_summed = CHECKSUM_NONE;
  		skb->csum_level = 0;
  	}
  }
  
  /* Check if we need to perform checksum complete validation.
   *
   * Returns true if checksum complete is needed, false otherwise
   * (either checksum is unnecessary or zero checksum is allowed).
   */
  static inline bool __skb_checksum_validate_needed(struct sk_buff *skb,
  						  bool zero_okay,
  						  __sum16 check)
  {
  	if (skb_csum_unnecessary(skb) || (zero_okay && !check)) {
  		skb->csum_valid = 1;
  		__skb_decr_checksum_unnecessary(skb);
  		return false;
  	}
  
  	return true;
  }
  
  /* For small packets <= CHECKSUM_BREAK perform checksum complete directly
   * in checksum_init.
   */
  #define CHECKSUM_BREAK 76
  
  /* Unset checksum-complete
   *
   * Unset checksum complete can be done when packet is being modified
   * (uncompressed for instance) and checksum-complete value is
   * invalidated.
   */
  static inline void skb_checksum_complete_unset(struct sk_buff *skb)
  {
  	if (skb->ip_summed == CHECKSUM_COMPLETE)
  		skb->ip_summed = CHECKSUM_NONE;
  }
  
  /* Validate (init) checksum based on checksum complete.
   *
   * Return values:
   *   0: checksum is validated or try to in skb_checksum_complete. In the latter
   *	case the ip_summed will not be CHECKSUM_UNNECESSARY and the pseudo
   *	checksum is stored in skb->csum for use in __skb_checksum_complete
   *   non-zero: value of invalid checksum
   *
   */
  static inline __sum16 __skb_checksum_validate_complete(struct sk_buff *skb,
  						       bool complete,
  						       __wsum psum)
  {
  	if (skb->ip_summed == CHECKSUM_COMPLETE) {
  		if (!csum_fold(csum_add(psum, skb->csum))) {
  			skb->csum_valid = 1;
  			return 0;
  		}
  	}
  
  	skb->csum = psum;
  
  	if (complete || skb->len <= CHECKSUM_BREAK) {
  		__sum16 csum;
  
  		csum = __skb_checksum_complete(skb);
  		skb->csum_valid = !csum;
  		return csum;
  	}
  
  	return 0;
  }
  
  static inline __wsum null_compute_pseudo(struct sk_buff *skb, int proto)
  {
  	return 0;
  }
  
  /* Perform checksum validate (init). Note that this is a macro since we only
   * want to calculate the pseudo header which is an input function if necessary.
   * First we try to validate without any computation (checksum unnecessary) and
   * then calculate based on checksum complete calling the function to compute
   * pseudo header.
   *
   * Return values:
   *   0: checksum is validated or try to in skb_checksum_complete
   *   non-zero: value of invalid checksum
   */
  #define __skb_checksum_validate(skb, proto, complete,			\
  				zero_okay, check, compute_pseudo)	\
  ({									\
  	__sum16 __ret = 0;						\
  	skb->csum_valid = 0;						\
  	if (__skb_checksum_validate_needed(skb, zero_okay, check))	\
  		__ret = __skb_checksum_validate_complete(skb,		\
  				complete, compute_pseudo(skb, proto));	\
  	__ret;								\
  })
  
  #define skb_checksum_init(skb, proto, compute_pseudo)			\
  	__skb_checksum_validate(skb, proto, false, false, 0, compute_pseudo)
  
  #define skb_checksum_init_zero_check(skb, proto, check, compute_pseudo)	\
  	__skb_checksum_validate(skb, proto, false, true, check, compute_pseudo)
  
  #define skb_checksum_validate(skb, proto, compute_pseudo)		\
  	__skb_checksum_validate(skb, proto, true, false, 0, compute_pseudo)
  
  #define skb_checksum_validate_zero_check(skb, proto, check,		\
  					 compute_pseudo)		\
  	__skb_checksum_validate(skb, proto, true, true, check, compute_pseudo)
  
  #define skb_checksum_simple_validate(skb)				\
  	__skb_checksum_validate(skb, 0, true, false, 0, null_compute_pseudo)
  
  static inline bool __skb_checksum_convert_check(struct sk_buff *skb)
  {
  	return (skb->ip_summed == CHECKSUM_NONE && skb->csum_valid);
  }
  
  static inline void __skb_checksum_convert(struct sk_buff *skb, __wsum pseudo)
  {
  	skb->csum = ~pseudo;
  	skb->ip_summed = CHECKSUM_COMPLETE;
  }
  
  #define skb_checksum_try_convert(skb, proto, compute_pseudo)	\
  do {									\
  	if (__skb_checksum_convert_check(skb))				\
  		__skb_checksum_convert(skb, compute_pseudo(skb, proto)); \
  } while (0)
  
  static inline void skb_remcsum_adjust_partial(struct sk_buff *skb, void *ptr,
  					      u16 start, u16 offset)
  {
  	skb->ip_summed = CHECKSUM_PARTIAL;
  	skb->csum_start = ((unsigned char *)ptr + start) - skb->head;
  	skb->csum_offset = offset - start;
  }
  
  /* Update skbuf and packet to reflect the remote checksum offload operation.
   * When called, ptr indicates the starting point for skb->csum when
   * ip_summed is CHECKSUM_COMPLETE. If we need create checksum complete
   * here, skb_postpull_rcsum is done so skb->csum start is ptr.
   */
  static inline void skb_remcsum_process(struct sk_buff *skb, void *ptr,
  				       int start, int offset, bool nopartial)
  {
  	__wsum delta;
  
  	if (!nopartial) {
  		skb_remcsum_adjust_partial(skb, ptr, start, offset);
  		return;
  	}
  
  	 if (unlikely(skb->ip_summed != CHECKSUM_COMPLETE)) {
  		__skb_checksum_complete(skb);
  		skb_postpull_rcsum(skb, skb->data, ptr - (void *)skb->data);
  	}
  
  	delta = remcsum_adjust(ptr, skb->csum, start, offset);
  
  	/* Adjust skb->csum since we changed the packet */
  	skb->csum = csum_add(skb->csum, delta);
  }
  
  static inline struct nf_conntrack *skb_nfct(const struct sk_buff *skb)
  {
  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  	return (void *)(skb->_nfct & NFCT_PTRMASK);
  #else
  	return NULL;
  #endif
  }
  
  static inline unsigned long skb_get_nfct(const struct sk_buff *skb)
  {
  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  	return skb->_nfct;
  #else
  	return 0UL;
  #endif
  }
  
  static inline void skb_set_nfct(struct sk_buff *skb, unsigned long nfct)
  {
  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  	skb->_nfct = nfct;
  #endif
  }
  
  #ifdef CONFIG_SKB_EXTENSIONS
  enum skb_ext_id {
  #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
  	SKB_EXT_BRIDGE_NF,
  #endif
  #ifdef CONFIG_XFRM
  	SKB_EXT_SEC_PATH,
  #endif
  #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
  	TC_SKB_EXT,
  #endif
  #if IS_ENABLED(CONFIG_MPTCP)
  	SKB_EXT_MPTCP,
  #endif
  	SKB_EXT_NUM, /* must be last */
  };
  
  /**
   *	struct skb_ext - sk_buff extensions
   *	@refcnt: 1 on allocation, deallocated on 0
   *	@offset: offset to add to @data to obtain extension address
   *	@chunks: size currently allocated, stored in SKB_EXT_ALIGN_SHIFT units
   *	@data: start of extension data, variable sized
   *
   *	Note: offsets/lengths are stored in chunks of 8 bytes, this allows
   *	to use 'u8' types while allowing up to 2kb worth of extension data.
   */
  struct skb_ext {
  	refcount_t refcnt;
  	u8 offset[SKB_EXT_NUM]; /* in chunks of 8 bytes */
  	u8 chunks;		/* same */
  	char data[] __aligned(8);
  };
  
  struct skb_ext *__skb_ext_alloc(gfp_t flags);
  void *__skb_ext_set(struct sk_buff *skb, enum skb_ext_id id,
  		    struct skb_ext *ext);
  void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id);
  void __skb_ext_del(struct sk_buff *skb, enum skb_ext_id id);
  void __skb_ext_put(struct skb_ext *ext);
  
  static inline void skb_ext_put(struct sk_buff *skb)
  {
  	if (skb->active_extensions)
  		__skb_ext_put(skb->extensions);
  }
  
  static inline void __skb_ext_copy(struct sk_buff *dst,
  				  const struct sk_buff *src)
  {
  	dst->active_extensions = src->active_extensions;
  
  	if (src->active_extensions) {
  		struct skb_ext *ext = src->extensions;
  
  		refcount_inc(&ext->refcnt);
  		dst->extensions = ext;
  	}
  }
  
  static inline void skb_ext_copy(struct sk_buff *dst, const struct sk_buff *src)
  {
  	skb_ext_put(dst);
  	__skb_ext_copy(dst, src);
  }
  
  static inline bool __skb_ext_exist(const struct skb_ext *ext, enum skb_ext_id i)
  {
  	return !!ext->offset[i];
  }
  
  static inline bool skb_ext_exist(const struct sk_buff *skb, enum skb_ext_id id)
  {
  	return skb->active_extensions & (1 << id);
  }
  
  static inline void skb_ext_del(struct sk_buff *skb, enum skb_ext_id id)
  {
  	if (skb_ext_exist(skb, id))
  		__skb_ext_del(skb, id);
  }
  
  static inline void *skb_ext_find(const struct sk_buff *skb, enum skb_ext_id id)
  {
  	if (skb_ext_exist(skb, id)) {
  		struct skb_ext *ext = skb->extensions;
  
  		return (void *)ext + (ext->offset[id] << 3);
  	}
  
  	return NULL;
  }
  
  static inline void skb_ext_reset(struct sk_buff *skb)
  {
  	if (unlikely(skb->active_extensions)) {
  		__skb_ext_put(skb->extensions);
  		skb->active_extensions = 0;
  	}
  }
  
  static inline bool skb_has_extensions(struct sk_buff *skb)
  {
  	return unlikely(skb->active_extensions);
  }
  #else
  static inline void skb_ext_put(struct sk_buff *skb) {}
  static inline void skb_ext_reset(struct sk_buff *skb) {}
  static inline void skb_ext_del(struct sk_buff *skb, int unused) {}
  static inline void __skb_ext_copy(struct sk_buff *d, const struct sk_buff *s) {}
  static inline void skb_ext_copy(struct sk_buff *dst, const struct sk_buff *s) {}
  static inline bool skb_has_extensions(struct sk_buff *skb) { return false; }
  #endif /* CONFIG_SKB_EXTENSIONS */
  
  static inline void nf_reset_ct(struct sk_buff *skb)
  {
  #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
  	nf_conntrack_put(skb_nfct(skb));
  	skb->_nfct = 0;
  #endif
  }
  
  static inline void nf_reset_trace(struct sk_buff *skb)
  {
  #if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE) || defined(CONFIG_NF_TABLES)
  	skb->nf_trace = 0;
  #endif
  }
  
  static inline void ipvs_reset(struct sk_buff *skb)
  {
  #if IS_ENABLED(CONFIG_IP_VS)
  	skb->ipvs_property = 0;
  #endif
  }
  
  /* Note: This doesn't put any conntrack info in dst. */
  static inline void __nf_copy(struct sk_buff *dst, const struct sk_buff *src,
  			     bool copy)
  {
  #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
  	dst->_nfct = src->_nfct;
  	nf_conntrack_get(skb_nfct(src));
  #endif
  #if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE) || defined(CONFIG_NF_TABLES)
  	if (copy)
  		dst->nf_trace = src->nf_trace;
  #endif
  }
  
  static inline void nf_copy(struct sk_buff *dst, const struct sk_buff *src)
  {
  #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
  	nf_conntrack_put(skb_nfct(dst));
  #endif
  	__nf_copy(dst, src, true);
  }
  
  #ifdef CONFIG_NETWORK_SECMARK
  static inline void skb_copy_secmark(struct sk_buff *to, const struct sk_buff *from)
  {
  	to->secmark = from->secmark;
  }
  
  static inline void skb_init_secmark(struct sk_buff *skb)
  {
  	skb->secmark = 0;
  }
  #else
  static inline void skb_copy_secmark(struct sk_buff *to, const struct sk_buff *from)
  { }
  
  static inline void skb_init_secmark(struct sk_buff *skb)
  { }
  #endif
  
  static inline int secpath_exists(const struct sk_buff *skb)
  {
  #ifdef CONFIG_XFRM
  	return skb_ext_exist(skb, SKB_EXT_SEC_PATH);
  #else
  	return 0;
  #endif
  }
  
  static inline bool skb_irq_freeable(const struct sk_buff *skb)
  {
  	return !skb->destructor &&
  		!secpath_exists(skb) &&
  		!skb_nfct(skb) &&
  		!skb->_skb_refdst &&
  		!skb_has_frag_list(skb);
  }
  
  static inline void skb_set_queue_mapping(struct sk_buff *skb, u16 queue_mapping)
  {
  	skb->queue_mapping = queue_mapping;
  }
  
  static inline u16 skb_get_queue_mapping(const struct sk_buff *skb)
  {
  	return skb->queue_mapping;
  }
  
  static inline void skb_copy_queue_mapping(struct sk_buff *to, const struct sk_buff *from)
  {
  	to->queue_mapping = from->queue_mapping;
  }
  
  static inline void skb_record_rx_queue(struct sk_buff *skb, u16 rx_queue)
  {
  	skb->queue_mapping = rx_queue + 1;
  }
  
  static inline u16 skb_get_rx_queue(const struct sk_buff *skb)
  {
  	return skb->queue_mapping - 1;
  }
  
  static inline bool skb_rx_queue_recorded(const struct sk_buff *skb)
  {
  	return skb->queue_mapping != 0;
  }
  
  static inline void skb_set_dst_pending_confirm(struct sk_buff *skb, u32 val)
  {
  	skb->dst_pending_confirm = val;
  }
  
  static inline bool skb_get_dst_pending_confirm(const struct sk_buff *skb)
  {
  	return skb->dst_pending_confirm != 0;
  }
  
  static inline struct sec_path *skb_sec_path(const struct sk_buff *skb)
  {
  #ifdef CONFIG_XFRM
  	return skb_ext_find(skb, SKB_EXT_SEC_PATH);
  #else
  	return NULL;
  #endif
  }
  
  /* Keeps track of mac header offset relative to skb->head.
   * It is useful for TSO of Tunneling protocol. e.g. GRE.
   * For non-tunnel skb it points to skb_mac_header() and for
   * tunnel skb it points to outer mac header.
   * Keeps track of level of encapsulation of network headers.
   */
  struct skb_gso_cb {
  	union {
  		int	mac_offset;
  		int	data_offset;
  	};
  	int	encap_level;
  	__wsum	csum;
  	__u16	csum_start;
  };
  #define SKB_GSO_CB_OFFSET	32
  #define SKB_GSO_CB(skb) ((struct skb_gso_cb *)((skb)->cb + SKB_GSO_CB_OFFSET))
  
  static inline int skb_tnl_header_len(const struct sk_buff *inner_skb)
  {
  	return (skb_mac_header(inner_skb) - inner_skb->head) -
  		SKB_GSO_CB(inner_skb)->mac_offset;
  }
  
  static inline int gso_pskb_expand_head(struct sk_buff *skb, int extra)
  {
  	int new_headroom, headroom;
  	int ret;
  
  	headroom = skb_headroom(skb);
  	ret = pskb_expand_head(skb, extra, 0, GFP_ATOMIC);
  	if (ret)
  		return ret;
  
  	new_headroom = skb_headroom(skb);
  	SKB_GSO_CB(skb)->mac_offset += (new_headroom - headroom);
  	return 0;
  }
  
  static inline void gso_reset_checksum(struct sk_buff *skb, __wsum res)
  {
  	/* Do not update partial checksums if remote checksum is enabled. */
  	if (skb->remcsum_offload)
  		return;
  
  	SKB_GSO_CB(skb)->csum = res;
  	SKB_GSO_CB(skb)->csum_start = skb_checksum_start(skb) - skb->head;
  }
  
  /* Compute the checksum for a gso segment. First compute the checksum value
   * from the start of transport header to SKB_GSO_CB(skb)->csum_start, and
   * then add in skb->csum (checksum from csum_start to end of packet).
   * skb->csum and csum_start are then updated to reflect the checksum of the
   * resultant packet starting from the transport header-- the resultant checksum
   * is in the res argument (i.e. normally zero or ~ of checksum of a pseudo
   * header.
   */
  static inline __sum16 gso_make_checksum(struct sk_buff *skb, __wsum res)
  {
  	unsigned char *csum_start = skb_transport_header(skb);
  	int plen = (skb->head + SKB_GSO_CB(skb)->csum_start) - csum_start;
  	__wsum partial = SKB_GSO_CB(skb)->csum;
  
  	SKB_GSO_CB(skb)->csum = res;
  	SKB_GSO_CB(skb)->csum_start = csum_start - skb->head;
  
  	return csum_fold(csum_partial(csum_start, plen, partial));
  }
  
  static inline bool skb_is_gso(const struct sk_buff *skb)
  {
  	return skb_shinfo(skb)->gso_size;
  }
  
  /* Note: Should be called only if skb_is_gso(skb) is true */
  static inline bool skb_is_gso_v6(const struct sk_buff *skb)
  {
  	return skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6;
  }
  
  /* Note: Should be called only if skb_is_gso(skb) is true */
  static inline bool skb_is_gso_sctp(const struct sk_buff *skb)
  {
  	return skb_shinfo(skb)->gso_type & SKB_GSO_SCTP;
  }
  
  /* Note: Should be called only if skb_is_gso(skb) is true */
  static inline bool skb_is_gso_tcp(const struct sk_buff *skb)
  {
  	return skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6);
  }
  
  static inline void skb_gso_reset(struct sk_buff *skb)
  {
  	skb_shinfo(skb)->gso_size = 0;
  	skb_shinfo(skb)->gso_segs = 0;
  	skb_shinfo(skb)->gso_type = 0;
  }
  
  static inline void skb_increase_gso_size(struct skb_shared_info *shinfo,
  					 u16 increment)
  {
  	if (WARN_ON_ONCE(shinfo->gso_size == GSO_BY_FRAGS))
  		return;
  	shinfo->gso_size += increment;
  }
  
  static inline void skb_decrease_gso_size(struct skb_shared_info *shinfo,
  					 u16 decrement)
  {
  	if (WARN_ON_ONCE(shinfo->gso_size == GSO_BY_FRAGS))
  		return;
  	shinfo->gso_size -= decrement;
  }
  
  void __skb_warn_lro_forwarding(const struct sk_buff *skb);
  
  static inline bool skb_warn_if_lro(const struct sk_buff *skb)
  {
  	/* LRO sets gso_size but not gso_type, whereas if GSO is really
  	 * wanted then gso_type will be set. */
  	const struct skb_shared_info *shinfo = skb_shinfo(skb);
  
  	if (skb_is_nonlinear(skb) && shinfo->gso_size != 0 &&
  	    unlikely(shinfo->gso_type == 0)) {
  		__skb_warn_lro_forwarding(skb);
  		return true;
  	}
  	return false;
  }
  
  static inline void skb_forward_csum(struct sk_buff *skb)
  {
  	/* Unfortunately we don't support this one.  Any brave souls? */
  	if (skb->ip_summed == CHECKSUM_COMPLETE)
  		skb->ip_summed = CHECKSUM_NONE;
  }
  
  /**
   * skb_checksum_none_assert - make sure skb ip_summed is CHECKSUM_NONE
   * @skb: skb to check
   *
   * fresh skbs have their ip_summed set to CHECKSUM_NONE.
   * Instead of forcing ip_summed to CHECKSUM_NONE, we can
   * use this helper, to document places where we make this assertion.
   */
  static inline void skb_checksum_none_assert(const struct sk_buff *skb)
  {
  #ifdef DEBUG
  	BUG_ON(skb->ip_summed != CHECKSUM_NONE);
  #endif
  }
  
  bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
  
  int skb_checksum_setup(struct sk_buff *skb, bool recalculate);
  struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
  				     unsigned int transport_len,
  				     __sum16(*skb_chkf)(struct sk_buff *skb));
  
  /**
   * skb_head_is_locked - Determine if the skb->head is locked down
   * @skb: skb to check
   *
   * The head on skbs build around a head frag can be removed if they are
   * not cloned.  This function returns true if the skb head is locked down
   * due to either being allocated via kmalloc, or by being a clone with
   * multiple references to the head.
   */
  static inline bool skb_head_is_locked(const struct sk_buff *skb)
  {
  	return !skb->head_frag || skb_cloned(skb);
  }
  
  /* Local Checksum Offload.
   * Compute outer checksum based on the assumption that the
   * inner checksum will be offloaded later.
   * See Documentation/networking/checksum-offloads.rst for
   * explanation of how this works.
   * Fill in outer checksum adjustment (e.g. with sum of outer
   * pseudo-header) before calling.
   * Also ensure that inner checksum is in linear data area.
   */
  static inline __wsum lco_csum(struct sk_buff *skb)
  {
  	unsigned char *csum_start = skb_checksum_start(skb);
  	unsigned char *l4_hdr = skb_transport_header(skb);
  	__wsum partial;
  
  	/* Start with complement of inner checksum adjustment */
  	partial = ~csum_unfold(*(__force __sum16 *)(csum_start +
  						    skb->csum_offset));
  
  	/* Add in checksum of our headers (incl. outer checksum
  	 * adjustment filled in by caller) and return result.
  	 */
  	return csum_partial(l4_hdr, csum_start - l4_hdr, partial);
  }
  
  static inline bool skb_is_redirected(const struct sk_buff *skb)
  {
  #ifdef CONFIG_NET_REDIRECT
  	return skb->redirected;
  #else
  	return false;
  #endif
  }
  
  static inline void skb_set_redirected(struct sk_buff *skb, bool from_ingress)
  {
  #ifdef CONFIG_NET_REDIRECT
  	skb->redirected = 1;
  	skb->from_ingress = from_ingress;
  	if (skb->from_ingress)
  		skb->tstamp = 0;
  #endif
  }
  
  static inline void skb_reset_redirect(struct sk_buff *skb)
  {
  #ifdef CONFIG_NET_REDIRECT
  	skb->redirected = 0;
  #endif
  }
  
  #endif	/* __KERNEL__ */
  #endif	/* _LINUX_SKBUFF_H */
  